linux.git/kernel/bpf/verifier.c, branch v5.11.8 Clone of https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git bpf: Add sanity check for upper ptr_limit 2021-03-20T09:51:13+00:00 Piotr Krysiuk piotras@gmail.com 2021-03-16T08:47:02+00:00 d94b5b83f42d50bd847f848b56d3a2b70ec7004b commit 1b1597e64e1a610c7a96710fc4717158e98a08b3 upstream. Given we know the max possible value of ptr_limit at the time of retrieving the latter, add basic assertions, so that the verifier can bail out if anything looks odd and reject the program. Nothing triggered this so far, but it also does not hurt to have these. Signed-off-by: Piotr Krysiuk <piotras@gmail.com> Co-developed-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
commit 1b1597e64e1a610c7a96710fc4717158e98a08b3 upstream.

Given we know the max possible value of ptr_limit at the time of retrieving
the latter, add basic assertions, so that the verifier can bail out if
anything looks odd and reject the program. Nothing triggered this so far,
but it also does not hurt to have these.

Signed-off-by: Piotr Krysiuk <piotras@gmail.com>
Co-developed-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
bpf: Simplify alu_limit masking for pointer arithmetic 2021-03-20T09:51:13+00:00 Piotr Krysiuk piotras@gmail.com 2021-03-16T07:26:25+00:00 6bc7314a685952608e32e8776a39173130540d7f commit b5871dca250cd391885218b99cc015aca1a51aea upstream. Instead of having the mov32 with aux->alu_limit - 1 immediate, move this operation to retrieve_ptr_limit() instead to simplify the logic and to allow for subsequent sanity boundary checks inside retrieve_ptr_limit(). This avoids in future that at the time of the verifier masking rewrite we'd run into an underflow which would not sign extend due to the nature of mov32 instruction. Signed-off-by: Piotr Krysiuk <piotras@gmail.com> Co-developed-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
commit b5871dca250cd391885218b99cc015aca1a51aea upstream.

Instead of having the mov32 with aux->alu_limit - 1 immediate, move this
operation to retrieve_ptr_limit() instead to simplify the logic and to
allow for subsequent sanity boundary checks inside retrieve_ptr_limit().
This avoids in future that at the time of the verifier masking rewrite
we'd run into an underflow which would not sign extend due to the nature
of mov32 instruction.

Signed-off-by: Piotr Krysiuk <piotras@gmail.com>
Co-developed-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
bpf: Fix off-by-one for area size in creating mask to left 2021-03-20T09:51:13+00:00 Piotr Krysiuk piotras@gmail.com 2021-03-16T07:20:16+00:00 c4f3aa4343deccf5b8e1bfcc7c36224aaf3a8b26 commit 10d2bb2e6b1d8c4576c56a748f697dbeb8388899 upstream. retrieve_ptr_limit() computes the ptr_limit for registers with stack and map_value type. ptr_limit is the size of the memory area that is still valid / in-bounds from the point of the current position and direction of the operation (add / sub). This size will later be used for masking the operation such that attempting out-of-bounds access in the speculative domain is redirected to remain within the bounds of the current map value. When masking to the right the size is correct, however, when masking to the left, the size is off-by-one which would lead to an incorrect mask and thus incorrect arithmetic operation in the non-speculative domain. Piotr found that if the resulting alu_limit value is zero, then the BPF_MOV32_IMM() from the fixup_bpf_calls() rewrite will end up loading 0xffffffff into AX instead of sign-extending to the full 64 bit range, and as a result, this allows abuse for executing speculatively out-of- bounds loads against 4GB window of address space and thus extracting the contents of kernel memory via side-channel. Fixes: 979d63d50c0c ("bpf: prevent out of bounds speculation on pointer arithmetic") Signed-off-by: Piotr Krysiuk <piotras@gmail.com> Co-developed-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
commit 10d2bb2e6b1d8c4576c56a748f697dbeb8388899 upstream.

retrieve_ptr_limit() computes the ptr_limit for registers with stack and
map_value type. ptr_limit is the size of the memory area that is still
valid / in-bounds from the point of the current position and direction
of the operation (add / sub). This size will later be used for masking
the operation such that attempting out-of-bounds access in the speculative
domain is redirected to remain within the bounds of the current map value.

When masking to the right the size is correct, however, when masking to
the left, the size is off-by-one which would lead to an incorrect mask
and thus incorrect arithmetic operation in the non-speculative domain.
Piotr found that if the resulting alu_limit value is zero, then the
BPF_MOV32_IMM() from the fixup_bpf_calls() rewrite will end up loading
0xffffffff into AX instead of sign-extending to the full 64 bit range,
and as a result, this allows abuse for executing speculatively out-of-
bounds loads against 4GB window of address space and thus extracting the
contents of kernel memory via side-channel.

Fixes: 979d63d50c0c ("bpf: prevent out of bounds speculation on pointer arithmetic")
Signed-off-by: Piotr Krysiuk <piotras@gmail.com>
Co-developed-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
bpf: Prohibit alu ops for pointer types not defining ptr_limit 2021-03-20T09:51:13+00:00 Piotr Krysiuk piotras@gmail.com 2021-03-16T08:47:02+00:00 6bf7609666f6b2a9169c39c79a47ef8d6082afae commit f232326f6966cf2a1d1db7bc917a4ce5f9f55f76 upstream. The purpose of this patch is to streamline error propagation and in particular to propagate retrieve_ptr_limit() errors for pointer types that are not defining a ptr_limit such that register-based alu ops against these types can be rejected. The main rationale is that a gap has been identified by Piotr in the existing protection against speculatively out-of-bounds loads, for example, in case of ctx pointers, unprivileged programs can still perform pointer arithmetic. This can be abused to execute speculatively out-of-bounds loads without restrictions and thus extract contents of kernel memory. Fix this by rejecting unprivileged programs that attempt any pointer arithmetic on unprotected pointer types. The two affected ones are pointer to ctx as well as pointer to map. Field access to a modified ctx' pointer is rejected at a later point in time in the verifier, and 7c6967326267 ("bpf: Permit map_ptr arithmetic with opcode add and offset 0") only relevant for root-only use cases. Risk of unprivileged program breakage is considered very low. Fixes: 7c6967326267 ("bpf: Permit map_ptr arithmetic with opcode add and offset 0") Fixes: b2157399cc98 ("bpf: prevent out-of-bounds speculation") Signed-off-by: Piotr Krysiuk <piotras@gmail.com> Co-developed-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
commit f232326f6966cf2a1d1db7bc917a4ce5f9f55f76 upstream.

The purpose of this patch is to streamline error propagation and in particular
to propagate retrieve_ptr_limit() errors for pointer types that are not defining
a ptr_limit such that register-based alu ops against these types can be rejected.

The main rationale is that a gap has been identified by Piotr in the existing
protection against speculatively out-of-bounds loads, for example, in case of
ctx pointers, unprivileged programs can still perform pointer arithmetic. This
can be abused to execute speculatively out-of-bounds loads without restrictions
and thus extract contents of kernel memory.

Fix this by rejecting unprivileged programs that attempt any pointer arithmetic
on unprotected pointer types. The two affected ones are pointer to ctx as well
as pointer to map. Field access to a modified ctx' pointer is rejected at a
later point in time in the verifier, and 7c6967326267 ("bpf: Permit map_ptr
arithmetic with opcode add and offset 0") only relevant for root-only use cases.
Risk of unprivileged program breakage is considered very low.

Fixes: 7c6967326267 ("bpf: Permit map_ptr arithmetic with opcode add and offset 0")
Fixes: b2157399cc98 ("bpf: prevent out-of-bounds speculation")
Signed-off-by: Piotr Krysiuk <piotras@gmail.com>
Co-developed-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
bpf: Clear subreg_def for global function return values 2021-03-04T11:13:56+00:00 Ilya Leoshkevich iii@linux.ibm.com 2021-02-12T04:04:08+00:00 7c5fdd4de87dcd827cf82f808d5fc3726c1acaae [ Upstream commit 45159b27637b0fef6d5ddb86fc7c46b13c77960f ] test_global_func4 fails on s390 as reported by Yauheni in [1]. The immediate problem is that the zext code includes the instruction, whose result needs to be zero-extended, into the zero-extension patchlet, and if this instruction happens to be a branch, then its delta is not adjusted. As a result, the verifier rejects the program later. However, according to [2], as far as the verifier's algorithm is concerned and as specified by the insn_no_def() function, branching insns do not define anything. This includes call insns, even though one might argue that they define %r0. This means that the real problem is that zero extension kicks in at all. This happens because clear_caller_saved_regs() sets BPF_REG_0's subreg_def after global function calls. This can be fixed in many ways; this patch mimics what helper function call handling already does. [1] https://lore.kernel.org/bpf/20200903140542.156624-1-yauheni.kaliuta@redhat.com/ [2] https://lore.kernel.org/bpf/CAADnVQ+2RPKcftZw8d+B1UwB35cpBhpF5u3OocNh90D9pETPwg@mail.gmail.com/ Fixes: 51c39bb1d5d1 ("bpf: Introduce function-by-function verification") Reported-by: Yauheni Kaliuta <yauheni.kaliuta@redhat.com> Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Link: https://lore.kernel.org/bpf/20210212040408.90109-1-iii@linux.ibm.com Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit 45159b27637b0fef6d5ddb86fc7c46b13c77960f ]

test_global_func4 fails on s390 as reported by Yauheni in [1].

The immediate problem is that the zext code includes the instruction,
whose result needs to be zero-extended, into the zero-extension
patchlet, and if this instruction happens to be a branch, then its
delta is not adjusted. As a result, the verifier rejects the program
later.

However, according to [2], as far as the verifier's algorithm is
concerned and as specified by the insn_no_def() function, branching
insns do not define anything. This includes call insns, even though
one might argue that they define %r0.

This means that the real problem is that zero extension kicks in at
all. This happens because clear_caller_saved_regs() sets BPF_REG_0's
subreg_def after global function calls. This can be fixed in many
ways; this patch mimics what helper function call handling already
does.

  [1] https://lore.kernel.org/bpf/20200903140542.156624-1-yauheni.kaliuta@redhat.com/
  [2] https://lore.kernel.org/bpf/CAADnVQ+2RPKcftZw8d+B1UwB35cpBhpF5u3OocNh90D9pETPwg@mail.gmail.com/

Fixes: 51c39bb1d5d1 ("bpf: Introduce function-by-function verification")
Reported-by: Yauheni Kaliuta <yauheni.kaliuta@redhat.com>
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20210212040408.90109-1-iii@linux.ibm.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
bpf: Fix truncation handling for mod32 dst reg wrt zero 2021-02-26T09:08:37+00:00 Daniel Borkmann daniel@iogearbox.net 2021-02-10T13:14:42+00:00 55c262ea5d0f754648cd25aa73de081adaab07d9 commit 9b00f1b78809309163dda2d044d9e94a3c0248a3 upstream. Recently noticed that when mod32 with a known src reg of 0 is performed, then the dst register is 32-bit truncated in verifier: 0: R1=ctx(id=0,off=0,imm=0) R10=fp0 0: (b7) r0 = 0 1: R0_w=inv0 R1=ctx(id=0,off=0,imm=0) R10=fp0 1: (b7) r1 = -1 2: R0_w=inv0 R1_w=inv-1 R10=fp0 2: (b4) w2 = -1 3: R0_w=inv0 R1_w=inv-1 R2_w=inv4294967295 R10=fp0 3: (9c) w1 %= w0 4: R0_w=inv0 R1_w=inv(id=0,umax_value=4294967295,var_off=(0x0; 0xffffffff)) R2_w=inv4294967295 R10=fp0 4: (b7) r0 = 1 5: R0_w=inv1 R1_w=inv(id=0,umax_value=4294967295,var_off=(0x0; 0xffffffff)) R2_w=inv4294967295 R10=fp0 5: (1d) if r1 == r2 goto pc+1 R0_w=inv1 R1_w=inv(id=0,umax_value=4294967295,var_off=(0x0; 0xffffffff)) R2_w=inv4294967295 R10=fp0 6: R0_w=inv1 R1_w=inv(id=0,umax_value=4294967295,var_off=(0x0; 0xffffffff)) R2_w=inv4294967295 R10=fp0 6: (b7) r0 = 2 7: R0_w=inv2 R1_w=inv(id=0,umax_value=4294967295,var_off=(0x0; 0xffffffff)) R2_w=inv4294967295 R10=fp0 7: (95) exit 7: R0=inv1 R1=inv(id=0,umin_value=4294967295,umax_value=4294967295,var_off=(0x0; 0xffffffff)) R2=inv4294967295 R10=fp0 7: (95) exit However, as a runtime result, we get 2 instead of 1, meaning the dst register does not contain (u32)-1 in this case. The reason is fairly straight forward given the 0 test leaves the dst register as-is: # ./bpftool p d x i 23 0: (b7) r0 = 0 1: (b7) r1 = -1 2: (b4) w2 = -1 3: (16) if w0 == 0x0 goto pc+1 4: (9c) w1 %= w0 5: (b7) r0 = 1 6: (1d) if r1 == r2 goto pc+1 7: (b7) r0 = 2 8: (95) exit This was originally not an issue given the dst register was marked as completely unknown (aka 64 bit unknown). However, after 468f6eafa6c4 ("bpf: fix 32-bit ALU op verification") the verifier casts the register output to 32 bit, and hence it becomes 32 bit unknown. Note that for the case where the src register is unknown, the dst register is marked 64 bit unknown. After the fix, the register is truncated by the runtime and the test passes: # ./bpftool p d x i 23 0: (b7) r0 = 0 1: (b7) r1 = -1 2: (b4) w2 = -1 3: (16) if w0 == 0x0 goto pc+2 4: (9c) w1 %= w0 5: (05) goto pc+1 6: (bc) w1 = w1 7: (b7) r0 = 1 8: (1d) if r1 == r2 goto pc+1 9: (b7) r0 = 2 10: (95) exit Semantics also match with {R,W}x mod{64,32} 0 -> {R,W}x. Invalid div has always been {R,W}x div{64,32} 0 -> 0. Rewrites are as follows: mod32: mod64: (16) if w0 == 0x0 goto pc+2 (15) if r0 == 0x0 goto pc+1 (9c) w1 %= w0 (9f) r1 %= r0 (05) goto pc+1 (bc) w1 = w1 Fixes: 468f6eafa6c4 ("bpf: fix 32-bit ALU op verification") Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Reviewed-by: John Fastabend <john.fastabend@gmail.com> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
commit 9b00f1b78809309163dda2d044d9e94a3c0248a3 upstream.

Recently noticed that when mod32 with a known src reg of 0 is performed,
then the dst register is 32-bit truncated in verifier:

  0: R1=ctx(id=0,off=0,imm=0) R10=fp0
  0: (b7) r0 = 0
  1: R0_w=inv0 R1=ctx(id=0,off=0,imm=0) R10=fp0
  1: (b7) r1 = -1
  2: R0_w=inv0 R1_w=inv-1 R10=fp0
  2: (b4) w2 = -1
  3: R0_w=inv0 R1_w=inv-1 R2_w=inv4294967295 R10=fp0
  3: (9c) w1 %= w0
  4: R0_w=inv0 R1_w=inv(id=0,umax_value=4294967295,var_off=(0x0; 0xffffffff)) R2_w=inv4294967295 R10=fp0
  4: (b7) r0 = 1
  5: R0_w=inv1 R1_w=inv(id=0,umax_value=4294967295,var_off=(0x0; 0xffffffff)) R2_w=inv4294967295 R10=fp0
  5: (1d) if r1 == r2 goto pc+1
   R0_w=inv1 R1_w=inv(id=0,umax_value=4294967295,var_off=(0x0; 0xffffffff)) R2_w=inv4294967295 R10=fp0
  6: R0_w=inv1 R1_w=inv(id=0,umax_value=4294967295,var_off=(0x0; 0xffffffff)) R2_w=inv4294967295 R10=fp0
  6: (b7) r0 = 2
  7: R0_w=inv2 R1_w=inv(id=0,umax_value=4294967295,var_off=(0x0; 0xffffffff)) R2_w=inv4294967295 R10=fp0
  7: (95) exit
  7: R0=inv1 R1=inv(id=0,umin_value=4294967295,umax_value=4294967295,var_off=(0x0; 0xffffffff)) R2=inv4294967295 R10=fp0
  7: (95) exit

However, as a runtime result, we get 2 instead of 1, meaning the dst
register does not contain (u32)-1 in this case. The reason is fairly
straight forward given the 0 test leaves the dst register as-is:

  # ./bpftool p d x i 23
   0: (b7) r0 = 0
   1: (b7) r1 = -1
   2: (b4) w2 = -1
   3: (16) if w0 == 0x0 goto pc+1
   4: (9c) w1 %= w0
   5: (b7) r0 = 1
   6: (1d) if r1 == r2 goto pc+1
   7: (b7) r0 = 2
   8: (95) exit

This was originally not an issue given the dst register was marked as
completely unknown (aka 64 bit unknown). However, after 468f6eafa6c4
("bpf: fix 32-bit ALU op verification") the verifier casts the register
output to 32 bit, and hence it becomes 32 bit unknown. Note that for
the case where the src register is unknown, the dst register is marked
64 bit unknown. After the fix, the register is truncated by the runtime
and the test passes:

  # ./bpftool p d x i 23
   0: (b7) r0 = 0
   1: (b7) r1 = -1
   2: (b4) w2 = -1
   3: (16) if w0 == 0x0 goto pc+2
   4: (9c) w1 %= w0
   5: (05) goto pc+1
   6: (bc) w1 = w1
   7: (b7) r0 = 1
   8: (1d) if r1 == r2 goto pc+1
   9: (b7) r0 = 2
  10: (95) exit

Semantics also match with {R,W}x mod{64,32} 0 -> {R,W}x. Invalid div
has always been {R,W}x div{64,32} 0 -> 0. Rewrites are as follows:

  mod32:                            mod64:

  (16) if w0 == 0x0 goto pc+2       (15) if r0 == 0x0 goto pc+1
  (9c) w1 %= w0                     (9f) r1 %= r0
  (05) goto pc+1
  (bc) w1 = w1

Fixes: 468f6eafa6c4 ("bpf: fix 32-bit ALU op verification")
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
bpf: Fix 32 bit src register truncation on div/mod 2021-02-10T00:32:40+00:00 Daniel Borkmann daniel@iogearbox.net 2021-02-09T18:46:10+00:00 e88b2c6e5a4d9ce30d75391e4d950da74bb2bd90 While reviewing a different fix, John and I noticed an oddity in one of the BPF program dumps that stood out, for example: # bpftool p d x i 13 0: (b7) r0 = 808464450 1: (b4) w4 = 808464432 2: (bc) w0 = w0 3: (15) if r0 == 0x0 goto pc+1 4: (9c) w4 %= w0 [...] In line 2 we noticed that the mov32 would 32 bit truncate the original src register for the div/mod operation. While for the two operations the dst register is typically marked unknown e.g. from adjust_scalar_min_max_vals() the src register is not, and thus verifier keeps tracking original bounds, simplified: 0: R1=ctx(id=0,off=0,imm=0) R10=fp0 0: (b7) r0 = -1 1: R0_w=invP-1 R1=ctx(id=0,off=0,imm=0) R10=fp0 1: (b7) r1 = -1 2: R0_w=invP-1 R1_w=invP-1 R10=fp0 2: (3c) w0 /= w1 3: R0_w=invP(id=0,umax_value=4294967295,var_off=(0x0; 0xffffffff)) R1_w=invP-1 R10=fp0 3: (77) r1 >>= 32 4: R0_w=invP(id=0,umax_value=4294967295,var_off=(0x0; 0xffffffff)) R1_w=invP4294967295 R10=fp0 4: (bf) r0 = r1 5: R0_w=invP4294967295 R1_w=invP4294967295 R10=fp0 5: (95) exit processed 6 insns (limit 1000000) max_states_per_insn 0 total_states 0 peak_states 0 mark_read 0 Runtime result of r0 at exit is 0 instead of expected -1. Remove the verifier mov32 src rewrite in div/mod and replace it with a jmp32 test instead. After the fix, we result in the following code generation when having dividend r1 and divisor r6: div, 64 bit: div, 32 bit: 0: (b7) r6 = 8 0: (b7) r6 = 8 1: (b7) r1 = 8 1: (b7) r1 = 8 2: (55) if r6 != 0x0 goto pc+2 2: (56) if w6 != 0x0 goto pc+2 3: (ac) w1 ^= w1 3: (ac) w1 ^= w1 4: (05) goto pc+1 4: (05) goto pc+1 5: (3f) r1 /= r6 5: (3c) w1 /= w6 6: (b7) r0 = 0 6: (b7) r0 = 0 7: (95) exit 7: (95) exit mod, 64 bit: mod, 32 bit: 0: (b7) r6 = 8 0: (b7) r6 = 8 1: (b7) r1 = 8 1: (b7) r1 = 8 2: (15) if r6 == 0x0 goto pc+1 2: (16) if w6 == 0x0 goto pc+1 3: (9f) r1 %= r6 3: (9c) w1 %= w6 4: (b7) r0 = 0 4: (b7) r0 = 0 5: (95) exit 5: (95) exit x86 in particular can throw a 'divide error' exception for div instruction not only for divisor being zero, but also for the case when the quotient is too large for the designated register. For the edx:eax and rdx:rax dividend pair it is not an issue in x86 BPF JIT since we always zero edx (rdx). Hence really the only protection needed is against divisor being zero. Fixes: 68fda450a7df ("bpf: fix 32-bit divide by zero") Co-developed-by: John Fastabend <john.fastabend@gmail.com> Signed-off-by: John Fastabend <john.fastabend@gmail.com> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> 
While reviewing a different fix, John and I noticed an oddity in one of the
BPF program dumps that stood out, for example:

  # bpftool p d x i 13
   0: (b7) r0 = 808464450
   1: (b4) w4 = 808464432
   2: (bc) w0 = w0
   3: (15) if r0 == 0x0 goto pc+1
   4: (9c) w4 %= w0
  [...]

In line 2 we noticed that the mov32 would 32 bit truncate the original src
register for the div/mod operation. While for the two operations the dst
register is typically marked unknown e.g. from adjust_scalar_min_max_vals()
the src register is not, and thus verifier keeps tracking original bounds,
simplified:

  0: R1=ctx(id=0,off=0,imm=0) R10=fp0
  0: (b7) r0 = -1
  1: R0_w=invP-1 R1=ctx(id=0,off=0,imm=0) R10=fp0
  1: (b7) r1 = -1
  2: R0_w=invP-1 R1_w=invP-1 R10=fp0
  2: (3c) w0 /= w1
  3: R0_w=invP(id=0,umax_value=4294967295,var_off=(0x0; 0xffffffff)) R1_w=invP-1 R10=fp0
  3: (77) r1 >>= 32
  4: R0_w=invP(id=0,umax_value=4294967295,var_off=(0x0; 0xffffffff)) R1_w=invP4294967295 R10=fp0
  4: (bf) r0 = r1
  5: R0_w=invP4294967295 R1_w=invP4294967295 R10=fp0
  5: (95) exit
  processed 6 insns (limit 1000000) max_states_per_insn 0 total_states 0 peak_states 0 mark_read 0

Runtime result of r0 at exit is 0 instead of expected -1. Remove the
verifier mov32 src rewrite in div/mod and replace it with a jmp32 test
instead. After the fix, we result in the following code generation when
having dividend r1 and divisor r6:

  div, 64 bit:                             div, 32 bit:

   0: (b7) r6 = 8                           0: (b7) r6 = 8
   1: (b7) r1 = 8                           1: (b7) r1 = 8
   2: (55) if r6 != 0x0 goto pc+2           2: (56) if w6 != 0x0 goto pc+2
   3: (ac) w1 ^= w1                         3: (ac) w1 ^= w1
   4: (05) goto pc+1                        4: (05) goto pc+1
   5: (3f) r1 /= r6                         5: (3c) w1 /= w6
   6: (b7) r0 = 0                           6: (b7) r0 = 0
   7: (95) exit                             7: (95) exit

  mod, 64 bit:                             mod, 32 bit:

   0: (b7) r6 = 8                           0: (b7) r6 = 8
   1: (b7) r1 = 8                           1: (b7) r1 = 8
   2: (15) if r6 == 0x0 goto pc+1           2: (16) if w6 == 0x0 goto pc+1
   3: (9f) r1 %= r6                         3: (9c) w1 %= w6
   4: (b7) r0 = 0                           4: (b7) r0 = 0
   5: (95) exit                             5: (95) exit

x86 in particular can throw a 'divide error' exception for div
instruction not only for divisor being zero, but also for the case
when the quotient is too large for the designated register. For the
edx:eax and rdx:rax dividend pair it is not an issue in x86 BPF JIT
since we always zero edx (rdx). Hence really the only protection
needed is against divisor being zero.

Fixes: 68fda450a7df ("bpf: fix 32-bit divide by zero")
Co-developed-by: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
bpf: Fix verifier jmp32 pruning decision logic 2021-02-10T00:31:46+00:00 Daniel Borkmann daniel@iogearbox.net 2021-02-05T19:48:21+00:00 fd675184fc7abfd1e1c52d23e8e900676b5a1c1a Anatoly has been fuzzing with kBdysch harness and reported a hang in one of the outcomes: func#0 @0 0: R1=ctx(id=0,off=0,imm=0) R10=fp0 0: (b7) r0 = 808464450 1: R0_w=invP808464450 R1=ctx(id=0,off=0,imm=0) R10=fp0 1: (b4) w4 = 808464432 2: R0_w=invP808464450 R1=ctx(id=0,off=0,imm=0) R4_w=invP808464432 R10=fp0 2: (9c) w4 %= w0 3: R0_w=invP808464450 R1=ctx(id=0,off=0,imm=0) R4_w=invP(id=0,umax_value=4294967295,var_off=(0x0; 0xffffffff)) R10=fp0 3: (66) if w4 s> 0x30303030 goto pc+0 R0_w=invP808464450 R1=ctx(id=0,off=0,imm=0) R4_w=invP(id=0,umax_value=4294967295,var_off=(0x0; 0xffffffff),s32_max_value=808464432) R10=fp0 4: R0_w=invP808464450 R1=ctx(id=0,off=0,imm=0) R4_w=invP(id=0,umax_value=4294967295,var_off=(0x0; 0xffffffff),s32_max_value=808464432) R10=fp0 4: (7f) r0 >>= r0 5: R0_w=invP(id=0) R1=ctx(id=0,off=0,imm=0) R4_w=invP(id=0,umax_value=4294967295,var_off=(0x0; 0xffffffff),s32_max_value=808464432) R10=fp0 5: (9c) w4 %= w0 6: R0_w=invP(id=0) R1=ctx(id=0,off=0,imm=0) R4_w=invP(id=0) R10=fp0 6: (66) if w0 s> 0x3030 goto pc+0 R0_w=invP(id=0,s32_max_value=12336) R1=ctx(id=0,off=0,imm=0) R4_w=invP(id=0) R10=fp0 7: R0=invP(id=0,s32_max_value=12336) R1=ctx(id=0,off=0,imm=0) R4=invP(id=0) R10=fp0 7: (d6) if w0 s<= 0x303030 goto pc+1 9: R0=invP(id=0,s32_max_value=12336) R1=ctx(id=0,off=0,imm=0) R4=invP(id=0) R10=fp0 9: (95) exit propagating r0 from 6 to 7: safe 4: R0_w=invP808464450 R1=ctx(id=0,off=0,imm=0) R4_w=invP(id=0,umin_value=808464433,umax_value=2147483647,var_off=(0x0; 0x7fffffff)) R10=fp0 4: (7f) r0 >>= r0 5: R0_w=invP(id=0) R1=ctx(id=0,off=0,imm=0) R4_w=invP(id=0,umin_value=808464433,umax_value=2147483647,var_off=(0x0; 0x7fffffff)) R10=fp0 5: (9c) w4 %= w0 6: R0_w=invP(id=0) R1=ctx(id=0,off=0,imm=0) R4_w=invP(id=0) R10=fp0 6: (66) if w0 s> 0x3030 goto pc+0 R0_w=invP(id=0,s32_max_value=12336) R1=ctx(id=0,off=0,imm=0) R4_w=invP(id=0) R10=fp0 propagating r0 7: safe propagating r0 from 6 to 7: safe processed 15 insns (limit 1000000) max_states_per_insn 0 total_states 1 peak_states 1 mark_read 1 The underlying program was xlated as follows: # bpftool p d x i 10 0: (b7) r0 = 808464450 1: (b4) w4 = 808464432 2: (bc) w0 = w0 3: (15) if r0 == 0x0 goto pc+1 4: (9c) w4 %= w0 5: (66) if w4 s> 0x30303030 goto pc+0 6: (7f) r0 >>= r0 7: (bc) w0 = w0 8: (15) if r0 == 0x0 goto pc+1 9: (9c) w4 %= w0 10: (66) if w0 s> 0x3030 goto pc+0 11: (d6) if w0 s<= 0x303030 goto pc+1 12: (05) goto pc-1 13: (95) exit The verifier rewrote original instructions it recognized as dead code with 'goto pc-1', but reality differs from verifier simulation in that we are actually able to trigger a hang due to hitting the 'goto pc-1' instructions. Taking a closer look at the verifier analysis, the reason is that it misjudges its pruning decision at the first 'from 6 to 7: safe' occasion. What happens is that while both old/cur registers are marked as precise, they get misjudged for the jmp32 case as range_within() yields true, meaning that the prior verification path with a wider register bound could be verified successfully and therefore the current path with a narrower register bound is deemed safe as well whereas in reality it's not. R0 old/cur path's bounds compare as follows: old: smin_value=0x8000000000000000,smax_value=0x7fffffffffffffff,umin_value=0x0,umax_value=0xffffffffffffffff,var_off=(0x0; 0xffffffffffffffff) cur: smin_value=0x8000000000000000,smax_value=0x7fffffff7fffffff,umin_value=0x0,umax_value=0xffffffff7fffffff,var_off=(0x0; 0xffffffff7fffffff) old: s32_min_value=0x80000000,s32_max_value=0x00003030,u32_min_value=0x00000000,u32_max_value=0xffffffff cur: s32_min_value=0x00003031,s32_max_value=0x7fffffff,u32_min_value=0x00003031,u32_max_value=0x7fffffff The 64 bit bounds generally look okay and while the information that got propagated from 32 to 64 bit looks correct as well, it's not precise enough for judging a conditional jmp32. Given the latter only operates on subregisters we also need to take these into account as well for a range_within() probe in order to be able to prune paths. Extending the range_within() constraint to both bounds will be able to tell us that the old signed 32 bit bounds are not wider than the cur signed 32 bit bounds. With the fix in place, the program will now verify the 'goto' branch case as it should have been: [...] 6: R0_w=invP(id=0) R1=ctx(id=0,off=0,imm=0) R4_w=invP(id=0) R10=fp0 6: (66) if w0 s> 0x3030 goto pc+0 R0_w=invP(id=0,s32_max_value=12336) R1=ctx(id=0,off=0,imm=0) R4_w=invP(id=0) R10=fp0 7: R0=invP(id=0,s32_max_value=12336) R1=ctx(id=0,off=0,imm=0) R4=invP(id=0) R10=fp0 7: (d6) if w0 s<= 0x303030 goto pc+1 9: R0=invP(id=0,s32_max_value=12336) R1=ctx(id=0,off=0,imm=0) R4=invP(id=0) R10=fp0 9: (95) exit 7: R0_w=invP(id=0,smax_value=9223372034707292159,umax_value=18446744071562067967,var_off=(0x0; 0xffffffff7fffffff),s32_min_value=12337,u32_min_value=12337,u32_max_value=2147483647) R1=ctx(id=0,off=0,imm=0) R4_w=invP(id=0) R10=fp0 7: (d6) if w0 s<= 0x303030 goto pc+1 R0_w=invP(id=0,smax_value=9223372034707292159,umax_value=18446744071562067967,var_off=(0x0; 0xffffffff7fffffff),s32_min_value=3158065,u32_min_value=3158065,u32_max_value=2147483647) R1=ctx(id=0,off=0,imm=0) R4_w=invP(id=0) R10=fp0 8: R0_w=invP(id=0,smax_value=9223372034707292159,umax_value=18446744071562067967,var_off=(0x0; 0xffffffff7fffffff),s32_min_value=3158065,u32_min_value=3158065,u32_max_value=2147483647) R1=ctx(id=0,off=0,imm=0) R4_w=invP(id=0) R10=fp0 8: (30) r0 = *(u8 *)skb[808464432] BPF_LD_[ABS|IND] uses reserved fields processed 11 insns (limit 1000000) max_states_per_insn 1 total_states 1 peak_states 1 mark_read 1 The bug is quite subtle in the sense that when verifier would determine that a given branch is dead code, it would (here: wrongly) remove these instructions from the program and hard-wire the taken branch for privileged programs instead of the 'goto pc-1' rewrites which will cause hard to debug problems. Fixes: 3f50f132d840 ("bpf: Verifier, do explicit ALU32 bounds tracking") Reported-by: Anatoly Trosinenko <anatoly.trosinenko@gmail.com> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Reviewed-by: John Fastabend <john.fastabend@gmail.com> Acked-by: Alexei Starovoitov <ast@kernel.org> 
Anatoly has been fuzzing with kBdysch harness and reported a hang in
one of the outcomes:

  func#0 @0
  0: R1=ctx(id=0,off=0,imm=0) R10=fp0
  0: (b7) r0 = 808464450
  1: R0_w=invP808464450 R1=ctx(id=0,off=0,imm=0) R10=fp0
  1: (b4) w4 = 808464432
  2: R0_w=invP808464450 R1=ctx(id=0,off=0,imm=0) R4_w=invP808464432 R10=fp0
  2: (9c) w4 %= w0
  3: R0_w=invP808464450 R1=ctx(id=0,off=0,imm=0) R4_w=invP(id=0,umax_value=4294967295,var_off=(0x0; 0xffffffff)) R10=fp0
  3: (66) if w4 s> 0x30303030 goto pc+0
   R0_w=invP808464450 R1=ctx(id=0,off=0,imm=0) R4_w=invP(id=0,umax_value=4294967295,var_off=(0x0; 0xffffffff),s32_max_value=808464432) R10=fp0
  4: R0_w=invP808464450 R1=ctx(id=0,off=0,imm=0) R4_w=invP(id=0,umax_value=4294967295,var_off=(0x0; 0xffffffff),s32_max_value=808464432) R10=fp0
  4: (7f) r0 >>= r0
  5: R0_w=invP(id=0) R1=ctx(id=0,off=0,imm=0) R4_w=invP(id=0,umax_value=4294967295,var_off=(0x0; 0xffffffff),s32_max_value=808464432) R10=fp0
  5: (9c) w4 %= w0
  6: R0_w=invP(id=0) R1=ctx(id=0,off=0,imm=0) R4_w=invP(id=0) R10=fp0
  6: (66) if w0 s> 0x3030 goto pc+0
   R0_w=invP(id=0,s32_max_value=12336) R1=ctx(id=0,off=0,imm=0) R4_w=invP(id=0) R10=fp0
  7: R0=invP(id=0,s32_max_value=12336) R1=ctx(id=0,off=0,imm=0) R4=invP(id=0) R10=fp0
  7: (d6) if w0 s<= 0x303030 goto pc+1
  9: R0=invP(id=0,s32_max_value=12336) R1=ctx(id=0,off=0,imm=0) R4=invP(id=0) R10=fp0
  9: (95) exit
  propagating r0

  from 6 to 7: safe
  4: R0_w=invP808464450 R1=ctx(id=0,off=0,imm=0) R4_w=invP(id=0,umin_value=808464433,umax_value=2147483647,var_off=(0x0; 0x7fffffff)) R10=fp0
  4: (7f) r0 >>= r0
  5: R0_w=invP(id=0) R1=ctx(id=0,off=0,imm=0) R4_w=invP(id=0,umin_value=808464433,umax_value=2147483647,var_off=(0x0; 0x7fffffff)) R10=fp0
  5: (9c) w4 %= w0
  6: R0_w=invP(id=0) R1=ctx(id=0,off=0,imm=0) R4_w=invP(id=0) R10=fp0
  6: (66) if w0 s> 0x3030 goto pc+0
   R0_w=invP(id=0,s32_max_value=12336) R1=ctx(id=0,off=0,imm=0) R4_w=invP(id=0) R10=fp0
  propagating r0
  7: safe
  propagating r0

  from 6 to 7: safe
  processed 15 insns (limit 1000000) max_states_per_insn 0 total_states 1 peak_states 1 mark_read 1

The underlying program was xlated as follows:

  # bpftool p d x i 10
   0: (b7) r0 = 808464450
   1: (b4) w4 = 808464432
   2: (bc) w0 = w0
   3: (15) if r0 == 0x0 goto pc+1
   4: (9c) w4 %= w0
   5: (66) if w4 s> 0x30303030 goto pc+0
   6: (7f) r0 >>= r0
   7: (bc) w0 = w0
   8: (15) if r0 == 0x0 goto pc+1
   9: (9c) w4 %= w0
  10: (66) if w0 s> 0x3030 goto pc+0
  11: (d6) if w0 s<= 0x303030 goto pc+1
  12: (05) goto pc-1
  13: (95) exit

The verifier rewrote original instructions it recognized as dead code with
'goto pc-1', but reality differs from verifier simulation in that we are
actually able to trigger a hang due to hitting the 'goto pc-1' instructions.

Taking a closer look at the verifier analysis, the reason is that it misjudges
its pruning decision at the first 'from 6 to 7: safe' occasion. What happens
is that while both old/cur registers are marked as precise, they get misjudged
for the jmp32 case as range_within() yields true, meaning that the prior
verification path with a wider register bound could be verified successfully
and therefore the current path with a narrower register bound is deemed safe
as well whereas in reality it's not. R0 old/cur path's bounds compare as
follows:

  old: smin_value=0x8000000000000000,smax_value=0x7fffffffffffffff,umin_value=0x0,umax_value=0xffffffffffffffff,var_off=(0x0; 0xffffffffffffffff)
  cur: smin_value=0x8000000000000000,smax_value=0x7fffffff7fffffff,umin_value=0x0,umax_value=0xffffffff7fffffff,var_off=(0x0; 0xffffffff7fffffff)

  old: s32_min_value=0x80000000,s32_max_value=0x00003030,u32_min_value=0x00000000,u32_max_value=0xffffffff
  cur: s32_min_value=0x00003031,s32_max_value=0x7fffffff,u32_min_value=0x00003031,u32_max_value=0x7fffffff

The 64 bit bounds generally look okay and while the information that got
propagated from 32 to 64 bit looks correct as well, it's not precise enough
for judging a conditional jmp32. Given the latter only operates on subregisters
we also need to take these into account as well for a range_within() probe
in order to be able to prune paths. Extending the range_within() constraint
to both bounds will be able to tell us that the old signed 32 bit bounds are
not wider than the cur signed 32 bit bounds.

With the fix in place, the program will now verify the 'goto' branch case as
it should have been:

  [...]
  6: R0_w=invP(id=0) R1=ctx(id=0,off=0,imm=0) R4_w=invP(id=0) R10=fp0
  6: (66) if w0 s> 0x3030 goto pc+0
   R0_w=invP(id=0,s32_max_value=12336) R1=ctx(id=0,off=0,imm=0) R4_w=invP(id=0) R10=fp0
  7: R0=invP(id=0,s32_max_value=12336) R1=ctx(id=0,off=0,imm=0) R4=invP(id=0) R10=fp0
  7: (d6) if w0 s<= 0x303030 goto pc+1
  9: R0=invP(id=0,s32_max_value=12336) R1=ctx(id=0,off=0,imm=0) R4=invP(id=0) R10=fp0
  9: (95) exit

  7: R0_w=invP(id=0,smax_value=9223372034707292159,umax_value=18446744071562067967,var_off=(0x0; 0xffffffff7fffffff),s32_min_value=12337,u32_min_value=12337,u32_max_value=2147483647) R1=ctx(id=0,off=0,imm=0) R4_w=invP(id=0) R10=fp0
  7: (d6) if w0 s<= 0x303030 goto pc+1
   R0_w=invP(id=0,smax_value=9223372034707292159,umax_value=18446744071562067967,var_off=(0x0; 0xffffffff7fffffff),s32_min_value=3158065,u32_min_value=3158065,u32_max_value=2147483647) R1=ctx(id=0,off=0,imm=0) R4_w=invP(id=0) R10=fp0
  8: R0_w=invP(id=0,smax_value=9223372034707292159,umax_value=18446744071562067967,var_off=(0x0; 0xffffffff7fffffff),s32_min_value=3158065,u32_min_value=3158065,u32_max_value=2147483647) R1=ctx(id=0,off=0,imm=0) R4_w=invP(id=0) R10=fp0
  8: (30) r0 = *(u8 *)skb[808464432]
  BPF_LD_[ABS|IND] uses reserved fields
  processed 11 insns (limit 1000000) max_states_per_insn 1 total_states 1 peak_states 1 mark_read 1

The bug is quite subtle in the sense that when verifier would determine that
a given branch is dead code, it would (here: wrongly) remove these instructions
from the program and hard-wire the taken branch for privileged programs instead
of the 'goto pc-1' rewrites which will cause hard to debug problems.

Fixes: 3f50f132d840 ("bpf: Verifier, do explicit ALU32 bounds tracking")
Reported-by: Anatoly Trosinenko <anatoly.trosinenko@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
bpf: Fix verifier jsgt branch analysis on max bound 2021-02-10T00:31:45+00:00 Daniel Borkmann daniel@iogearbox.net 2021-02-05T16:20:14+00:00 ee114dd64c0071500345439fc79dd5e0f9d106ed Fix incorrect is_branch{32,64}_taken() analysis for the jsgt case. The return code for both will tell the caller whether a given conditional jump is taken or not, e.g. 1 means branch will be taken [for the involved registers] and the goto target will be executed, 0 means branch will not be taken and instead we fall-through to the next insn, and last but not least a -1 denotes that it is not known at verification time whether a branch will be taken or not. Now while the jsgt has the branch-taken case correct with reg->s32_min_value > sval, the branch-not-taken case is off-by-one when testing for reg->s32_max_value < sval since the branch will also be taken for reg->s32_max_value == sval. The jgt branch analysis, for example, gets this right. Fixes: 3f50f132d840 ("bpf: Verifier, do explicit ALU32 bounds tracking") Fixes: 4f7b3e82589e ("bpf: improve verifier branch analysis") Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Reviewed-by: John Fastabend <john.fastabend@gmail.com> Acked-by: Alexei Starovoitov <ast@kernel.org> 
Fix incorrect is_branch{32,64}_taken() analysis for the jsgt case. The return
code for both will tell the caller whether a given conditional jump is taken
or not, e.g. 1 means branch will be taken [for the involved registers] and the
goto target will be executed, 0 means branch will not be taken and instead we
fall-through to the next insn, and last but not least a -1 denotes that it is
not known at verification time whether a branch will be taken or not. Now while
the jsgt has the branch-taken case correct with reg->s32_min_value > sval, the
branch-not-taken case is off-by-one when testing for reg->s32_max_value < sval
since the branch will also be taken for reg->s32_max_value == sval. The jgt
branch analysis, for example, gets this right.

Fixes: 3f50f132d840 ("bpf: Verifier, do explicit ALU32 bounds tracking")
Fixes: 4f7b3e82589e ("bpf: improve verifier branch analysis")
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
bpf: Fix signed_{sub,add32}_overflows type handling 2021-01-20T16:19:40+00:00 Daniel Borkmann daniel@iogearbox.net 2021-01-19T23:24:24+00:00 bc895e8b2a64e502fbba72748d59618272052a8b Fix incorrect signed_{sub,add32}_overflows() input types (and a related buggy comment). It looks like this might have slipped in via copy/paste issue, also given prior to 3f50f132d840 ("bpf: Verifier, do explicit ALU32 bounds tracking") the signature of signed_sub_overflows() had s64 a and s64 b as its input args whereas now they are truncated to s32. Thus restore proper types. Also, the case of signed_add32_overflows() is not consistent to signed_sub32_overflows(). Both have s32 as inputs, therefore align the former. Fixes: 3f50f132d840 ("bpf: Verifier, do explicit ALU32 bounds tracking") Reported-by: De4dCr0w <sa516203@mail.ustc.edu.cn> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Reviewed-by: John Fastabend <john.fastabend@gmail.com> Acked-by: Alexei Starovoitov <ast@kernel.org> 
Fix incorrect signed_{sub,add32}_overflows() input types (and a related buggy
comment). It looks like this might have slipped in via copy/paste issue, also
given prior to 3f50f132d840 ("bpf: Verifier, do explicit ALU32 bounds tracking")
the signature of signed_sub_overflows() had s64 a and s64 b as its input args
whereas now they are truncated to s32. Thus restore proper types. Also, the case
of signed_add32_overflows() is not consistent to signed_sub32_overflows(). Both
have s32 as inputs, therefore align the former.

Fixes: 3f50f132d840 ("bpf: Verifier, do explicit ALU32 bounds tracking")
Reported-by: De4dCr0w <sa516203@mail.ustc.edu.cn>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>