linux.git/kernel/bpf, branch v6.18.21

bpf: Fix u32/s32 bounds when ranges cross min/max boundary

2026-04-02T11:23:00+00:00

[ Upstream commit fbc7aef517d8765e4c425d2792409bb9bf2e1f13 ]

Same as in __reg64_deduce_bounds(), refine s32/u32 ranges
in __reg32_deduce_bounds() in the following situations:

- s32 range crosses U32_MAX/0 boundary, positive part of the s32 range
  overlaps with u32 range:

  0                                                   U32_MAX
  |  [xxxxxxxxxxxxxx u32 range xxxxxxxxxxxxxx]              |
  |----------------------------|----------------------------|
  |xxxxx s32 range xxxxxxxxx]                       [xxxxxxx|
  0                     S32_MAX S32_MIN                    -1

- s32 range crosses U32_MAX/0 boundary, negative part of the s32 range
  overlaps with u32 range:

  0                                                   U32_MAX
  |              [xxxxxxxxxxxxxx u32 range xxxxxxxxxxxxxx]  |
  |----------------------------|----------------------------|
  |xxxxxxxxx]                       [xxxxxxxxxxxx s32 range |
  0                     S32_MAX S32_MIN                    -1

- No refinement if ranges overlap in two intervals.

This helps for e.g. consider the following program:

   call %[bpf_get_prandom_u32];
   w0 &= 0xffffffff;
   if w0 < 0x3 goto 1f;    // on fall-through u32 range [3..U32_MAX]
   if w0 s> 0x1 goto 1f;   // on fall-through s32 range [S32_MIN..1]
   if w0 s< 0x0 goto 1f;   // range can be narrowed to  [S32_MIN..-1]
   r10 = 0;
1: ...;

The reg_bounds.c selftest is updated to incorporate identical logic,
refinement based on non-overflowing range halves:

  ((x ∩ [0, smax]) ∩ (y ∩ [0, smax])) ∪
  ((x ∩ [smin,-1]) ∩ (y ∩ [smin,-1]))

Reported-by: Andrea Righi 
Reported-by: Emil Tsalapatis 
Closes: https://lore.kernel.org/bpf/aakqucg4vcujVwif@gpd4/T/
Reviewed-by: Emil Tsalapatis 
Acked-by: Shung-Hsi Yu 
Signed-off-by: Eduard Zingerman 
Link: https://lore.kernel.org/r/20260306-bpf-32-bit-range-overflow-v3-1-f7f67e060a6b@gmail.com
Signed-off-by: Alexei Starovoitov 
Signed-off-by: Sasha Levin

bpf: Fix unsound scalar forking in maybe_fork_scalars() for BPF_OR

2026-04-02T11:22:55+00:00

[ Upstream commit c845894ebd6fb43226b3118d6b017942550910c5 ]

maybe_fork_scalars() is called for both BPF_AND and BPF_OR when the
source operand is a constant.  When dst has signed range [-1, 0], it
forks the verifier state: the pushed path gets dst = 0, the current
path gets dst = -1.

For BPF_AND this is correct: 0 & K == 0.
For BPF_OR this is wrong:    0 | K == K, not 0.

The pushed path therefore tracks dst as 0 when the runtime value is K,
producing an exploitable verifier/runtime divergence that allows
out-of-bounds map access.

Fix this by passing env->insn_idx (instead of env->insn_idx + 1) to
push_stack(), so the pushed path re-executes the ALU instruction with
dst = 0 and naturally computes the correct result for any opcode.

Fixes: bffacdb80b93 ("bpf: Recognize special arithmetic shift in the verifier")
Signed-off-by: Daniel Wade 
Reviewed-by: Amery Hung 
Acked-by: Eduard Zingerman 
Link: https://lore.kernel.org/r/20260314021521.128361-2-danjwade95@gmail.com
Signed-off-by: Alexei Starovoitov 
Signed-off-by: Sasha Levin

bpf: Fix undefined behavior in interpreter sdiv/smod for INT_MIN

2026-04-02T11:22:55+00:00

[ Upstream commit c77b30bd1dcb61f66c640ff7d2757816210c7cb0 ]

The BPF interpreter's signed 32-bit division and modulo handlers use
the kernel abs() macro on s32 operands. The abs() macro documentation
(include/linux/math.h) explicitly states the result is undefined when
the input is the type minimum. When DST contains S32_MIN (0x80000000),
abs((s32)DST) triggers undefined behavior and returns S32_MIN unchanged
on arm64/x86. This value is then sign-extended to u64 as
0xFFFFFFFF80000000, causing do_div() to compute the wrong result.

The verifier's abstract interpretation (scalar32_min_max_sdiv) computes
the mathematically correct result for range tracking, creating a
verifier/interpreter mismatch that can be exploited for out-of-bounds
map value access.

Introduce abs_s32() which handles S32_MIN correctly by casting to u32
before negating, avoiding signed overflow entirely. Replace all 8
abs((s32)...) call sites in the interpreter's sdiv32/smod32 handlers.

s32 is the only affected case -- the s64 division/modulo handlers do
not use abs().

Fixes: ec0e2da95f72 ("bpf: Support new signed div/mod instructions.")
Acked-by: Yonghong Song 
Acked-by: Mykyta Yatsenko 
Signed-off-by: Jenny Guanni Qu 
Link: https://lore.kernel.org/r/20260311011116.2108005-2-qguanni@gmail.com
Signed-off-by: Alexei Starovoitov 
Signed-off-by: Sasha Levin

bpf: Fix exception exit lock checking for subprogs

2026-04-02T11:22:54+00:00

[ Upstream commit 6c2128505f61b504c79a20b89596feba61388112 ]

process_bpf_exit_full() passes check_lock = !curframe to
check_resource_leak(), which is false in cases when bpf_throw() is
called from a static subprog. This makes check_resource_leak() to skip
validation of active_rcu_locks, active_preempt_locks, and
active_irq_id on exception exits from subprogs.

At runtime bpf_throw() unwinds the stack via ORC without releasing any
user-acquired locks, which may cause various issues as the result.

Fix by setting check_lock = true for exception exits regardless of
curframe, since exceptions bypass all intermediate frame
cleanup. Update the error message prefix to "bpf_throw" for exception
exits to distinguish them from normal BPF_EXIT.

Fix reject_subprog_with_rcu_read_lock test which was previously
passing for the wrong reason. Test program returned directly from the
subprog call without closing the RCU section, so the error was
triggered by the unclosed RCU lock on normal exit, not by
bpf_throw. Update __msg annotations for affected tests to match the
new "bpf_throw" error prefix.

The spin_lock case is not affected because they are already checked [1]
at the call site in do_check_insn() before bpf_throw can run.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/kernel/bpf/verifier.c?h=v7.0-rc4#n21098

Assisted-by: Claude:claude-opus-4-6
Fixes: f18b03fabaa9 ("bpf: Implement BPF exceptions")
Signed-off-by: Ihor Solodrai
Acked-by: Yonghong Song
Acked-by: Kumar Kartikeya Dwivedi
Link: https://lore.kernel.org/r/20260320000809.643798-1-ihor.solodrai@linux.dev
Signed-off-by: Alexei Starovoitov
Signed-off-by: Sasha Levin

bpf: Release module BTF IDR before module unload

2026-04-02T11:22:54+00:00

[ Upstream commit 146bd2a87a65aa407bb17fac70d8d583d19aba06 ]

Gregory reported in [0] that the global_map_resize test when run in
repeatedly ends up failing during program load. This stems from the fact
that BTF reference has not dropped to zero after the previous run's
module is unloaded, and the older module's BTF is still discoverable and
visible. Later, in libbpf, load_module_btfs() will find the ID for this
stale BTF, open its fd, and then it will be used during program load
where later steps taking module reference using btf_try_get_module()
fail since the underlying module for the BTF is gone.

Logically, once a module is unloaded, it's associated BTF artifacts
should become hidden. The BTF object inside the kernel may still remain
alive as long its reference counts are alive, but it should no longer be
discoverable.

To fix this, let us call btf_free_id() from the MODULE_STATE_GOING case
for the module unload to free the BTF associated IDR entry, and disable
its discovery once module unload returns to user space. If a race
happens during unload, the outcome is non-deterministic anyway. However,
user space should be able to rely on the guarantee that once it has
synchronously established a successful module unload, no more stale
artifacts associated with this module can be obtained subsequently.

Note that we must be careful to not invoke btf_free_id() in btf_put()
when btf_is_module() is true now. There could be a window where the
module unload drops a non-terminal reference, frees the IDR, but the
same ID gets reused and the second unconditional btf_free_id() ends up
releasing an unrelated entry.

To avoid a special case for btf_is_module() case, set btf->id to zero to
make btf_free_id() idempotent, such that we can unconditionally invoke it
from btf_put(), and also from the MODULE_STATE_GOING case. Since zero is
an invalid IDR, the idr_remove() should be a noop.

Note that we can be sure that by the time we reach final btf_put() for
btf_is_module() case, the btf_free_id() is already done, since the
module itself holds the BTF reference, and it will call this function
for the BTF before dropping its own reference.

  [0]: https://lore.kernel.org/bpf/cover.1773170190.git.grbell@redhat.com

Fixes: 36e68442d1af ("bpf: Load and verify kernel module BTFs")
Acked-by: Martin KaFai Lau 
Suggested-by: Martin KaFai Lau 
Reported-by: Gregory Bell 
Reviewed-by: Emil Tsalapatis 
Signed-off-by: Kumar Kartikeya Dwivedi 
Link: https://lore.kernel.org/r/20260312205307.1346991-1-memxor@gmail.com
Signed-off-by: Alexei Starovoitov 
Signed-off-by: Sasha Levin

bpf: Fix constant blinding for PROBE_MEM32 stores

2026-04-02T11:22:53+00:00

[ Upstream commit 2321a9596d2260310267622e0ad8fbfa6f95378f ]

BPF_ST | BPF_PROBE_MEM32 immediate stores are not handled by
bpf_jit_blind_insn(), allowing user-controlled 32-bit immediates to
survive unblinded into JIT-compiled native code when bpf_jit_harden >= 1.

The root cause is that convert_ctx_accesses() rewrites BPF_ST|BPF_MEM
to BPF_ST|BPF_PROBE_MEM32 for arena pointer stores during verification,
before bpf_jit_blind_constants() runs during JIT compilation. The
blinding switch only matches BPF_ST|BPF_MEM (mode 0x60), not
BPF_ST|BPF_PROBE_MEM32 (mode 0xa0). The instruction falls through
unblinded.

Add BPF_ST|BPF_PROBE_MEM32 cases to bpf_jit_blind_insn() alongside the
existing BPF_ST|BPF_MEM cases. The blinding transformation is identical:
load the blinded immediate into BPF_REG_AX via mov+xor, then convert
the immediate store to a register store (BPF_STX).

The rewritten STX instruction must preserve the BPF_PROBE_MEM32 mode so
the architecture JIT emits the correct arena addressing (R12-based on
x86-64). Cannot use the BPF_STX_MEM() macro here because it hardcodes
BPF_MEM mode; construct the instruction directly instead.

Fixes: 6082b6c328b5 ("bpf: Recognize addr_space_cast instruction in the verifier.")
Reviewed-by: Puranjay Mohan 
Reviewed-by: Emil Tsalapatis 
Signed-off-by: Sachin Kumar 
Acked-by: Daniel Borkmann 
Link: https://lore.kernel.org/r/Y6IT5VvNRchPBLI5D7JZHBzZrU9rb0ycRJPJzJSXGj7kJlX8RJwZFSM2YZjcDxoQKABkxt1T8Os2gi23PYyFuQe6KkZGWVyfz8K5afdy9ak=@protonmail.com
Signed-off-by: Alexei Starovoitov 
Signed-off-by: Sasha Levin

bpf: Reset register ID for BPF_END value tracking

2026-04-02T11:22:53+00:00

[ Upstream commit a3125bc01884431d30d731461634c8295b6f0529 ]

When a register undergoes a BPF_END (byte swap) operation, its scalar
value is mutated in-place. If this register previously shared a scalar ID
with another register (e.g., after an `r1 = r0` assignment), this tie must
be broken.

Currently, the verifier misses resetting `dst_reg->id` to 0 for BPF_END.
Consequently, if a conditional jump checks the swapped register, the
verifier incorrectly propagates the learned bounds to the linked register,
leading to false confidence in the linked register's value and potentially
allowing out-of-bounds memory accesses.

Fix this by explicitly resetting `dst_reg->id` to 0 in the BPF_END case
to break the scalar tie, similar to how BPF_NEG handles it via
`__mark_reg_known`.

Fixes: 9d2119984224 ("bpf: Add bitwise tracking for BPF_END")
Closes: https://lore.kernel.org/bpf/AMBPR06MB108683CFEB1CB8D9E02FC95ECF17EA@AMBPR06MB10868.eurprd06.prod.outlook.com/
Link: https://lore.kernel.org/bpf/4be25f7442a52244d0dd1abb47bc6750e57984c9.camel@gmail.com/
Reported-by: Guillaume Laporte 
Co-developed-by: Tianci Cao 
Signed-off-by: Tianci Cao 
Co-developed-by: Shenghao Yuan 
Signed-off-by: Shenghao Yuan 
Signed-off-by: Yazhou Tang 
Acked-by: Eduard Zingerman 
Link: https://lore.kernel.org/r/20260304083228.142016-2-tangyazhou@zju.edu.cn
Signed-off-by: Alexei Starovoitov 
Signed-off-by: Sasha Levin

bpf: drop kthread_exit from noreturn_deny

2026-03-19T15:08:51+00:00

commit 7fe44c4388146bdbb3c5932d81a26d9fa0fd3ec9 upstream.

kthread_exit became a macro to do_exit in commit 28aaa9c39945
("kthread: consolidate kthread exit paths to prevent use-after-free"),
so there is no kthread_exit function BTF ID to resolve. Remove it from
noreturn_deny to avoid resolve_btfids unresolved symbol warnings.

Signed-off-by: Christian Loehle 
Signed-off-by: Linus Torvalds 
Signed-off-by: Greg Kroah-Hartman

bpf: collect only live registers in linked regs

2026-03-12T11:10:02+00:00

[ Upstream commit 2658a1720a1944fbaeda937000ad2b3c3dfaf1bb ]

Fix an inconsistency between func_states_equal() and
collect_linked_regs():
- regsafe() uses check_ids() to verify that cached and current states
  have identical register id mapping.
- func_states_equal() calls regsafe() only for registers computed as
  live by compute_live_registers().
- clean_live_states() is supposed to remove dead registers from cached
  states, but it can skip states belonging to an iterator-based loop.
- collect_linked_regs() collects all registers sharing the same id,
  ignoring the marks computed by compute_live_registers().
  Linked registers are stored in the state's jump history.
- backtrack_insn() marks all linked registers for an instruction
  as precise whenever one of the linked registers is precise.

The above might lead to a scenario:
- There is an instruction I with register rY known to be dead at I.
- Instruction I is reached via two paths: first A, then B.
- On path A:
  - There is an id link between registers rX and rY.
  - Checkpoint C is created at I.
  - Linked register set {rX, rY} is saved to the jump history.
  - rX is marked as precise at I, causing both rX and rY
    to be marked precise at C.
- On path B:
  - There is no id link between registers rX and rY,
    otherwise register states are sub-states of those in C.
  - Because rY is dead at I, check_ids() returns true.
  - Current state is considered equal to checkpoint C,
    propagate_precision() propagates spurious precision
    mark for register rY along the path B.
  - Depending on a program, this might hit verifier_bug()
    in the backtrack_insn(), e.g. if rY ∈  [r1..r5]
    and backtrack_insn() spots a function call.

The reproducer program is in the next patch.
This was hit by sched_ext scx_lavd scheduler code.

Changes in tests:
- verifier_scalar_ids.c selftests need modification to preserve
  some registers as live for __msg() checks.
- exceptions_assert.c adjusted to match changes in the verifier log,
  R0 is dead after conditional instruction and thus does not get
  range.
- precise.c adjusted to match changes in the verifier log, register r9
  is dead after comparison and it's range is not important for test.

Reported-by: Emil Tsalapatis 
Fixes: 0fb3cf6110a5 ("bpf: use register liveness information for func_states_equal")
Signed-off-by: Eduard Zingerman 
Link: https://lore.kernel.org/r/20260306-linked-regs-and-propagate-precision-v1-1-18e859be570d@gmail.com
Signed-off-by: Alexei Starovoitov 
Signed-off-by: Sasha Levin

bpf: Fix a UAF issue in bpf_trampoline_link_cgroup_shim

2026-03-12T11:09:55+00:00

[ Upstream commit 56145d237385ca0e7ca9ff7b226aaf2eb8ef368b ]

The root cause of this bug is that when 'bpf_link_put' reduces the
refcount of 'shim_link->link.link' to zero, the resource is considered
released but may still be referenced via 'tr->progs_hlist' in
'cgroup_shim_find'. The actual cleanup of 'tr->progs_hlist' in
'bpf_shim_tramp_link_release' is deferred. During this window, another
process can cause a use-after-free via 'bpf_trampoline_link_cgroup_shim'.

Based on Martin KaFai Lau's suggestions, I have created a simple patch.

To fix this:
   Add an atomic non-zero check in 'bpf_trampoline_link_cgroup_shim'.
   Only increment the refcount if it is not already zero.

Testing:
   I verified the fix by adding a delay in
   'bpf_shim_tramp_link_release' to make the bug easier to trigger:

static void bpf_shim_tramp_link_release(struct bpf_link *link)
{
	/* ... */
	if (!shim_link->trampoline)
		return;

+	msleep(100);
	WARN_ON_ONCE(bpf_trampoline_unlink_prog(&shim_link->link,
		shim_link->trampoline, NULL));
	bpf_trampoline_put(shim_link->trampoline);
}

Before the patch, running a PoC easily reproduced the crash(almost 100%)
with a call trace similar to KaiyanM's report.
After the patch, the bug no longer occurs even after millions of
iterations.

Fixes: 69fd337a975c ("bpf: per-cgroup lsm flavor")
Reported-by: Kaiyan Mei 
Closes: https://lore.kernel.org/bpf/3c4ebb0b.46ff8.19abab8abe2.Coremail.kaiyanm@hust.edu.cn/
Signed-off-by: Lang Xu 
Signed-off-by: Martin KaFai Lau 
Link: https://patch.msgid.link/279EEE1BA1DDB49D+20260303095217.34436-1-xulang@uniontech.com
Signed-off-by: Sasha Levin