linux.git/arch/powerpc/kernel/process.c, branch v6.10-rc6

powerpc: Fix typos

2024-05-07T14:21:30+00:00

Fix typos, most reported by "codespell arch/powerpc".  Only touches
comments, no code changes.

Signed-off-by: Bjorn Helgaas 
Signed-off-by: Michael Ellerman 
Link: https://msgid.link/20240103231605.1801364-8-helgaas@kernel.org

powerpc/dexcr: Reset DEXCR value across exec

2024-05-03T10:46:51+00:00

Inheriting the DEXCR across exec can have security and usability
concerns. If a program is compiled with hash instructions it generally
expects to run with NPHIE enabled. But if the parent process disables
NPHIE then if it's not careful it will be disabled for any children too
and the protection offered by hash checks is basically worthless.

This patch introduces a per-process reset value that new execs in a
particular process tree are initialized with. This enables fine grained
control over what DEXCR value child processes run with by default.
For example, containers running legacy binaries that expect hash
instructions to act as NOPs could configure the reset value of the
container root to control the default reset value for all members of
the container.

Signed-off-by: Benjamin Gray 
[mpe: Add missing SPDX tag on dexcr.c]
Signed-off-by: Michael Ellerman 
Link: https://msgid.link/20240417112325.728010-4-bgray@linux.ibm.com

powerpc/dexcr: Track the DEXCR per-process

2024-05-03T10:46:51+00:00

Add capability to make the DEXCR act as a per-process SPR.

We do not yet have an interface for changing the values per task. We
also expect the kernel to use a single DEXCR value across all tasks
while in privileged state, so there is no need to synchronize after
changing it (the userspace aspects will synchronize upon returning to
userspace).

Signed-off-by: Benjamin Gray 
Signed-off-by: Michael Ellerman 
Link: https://msgid.link/20240417112325.728010-3-bgray@linux.ibm.com

KVM: PPC: Book3S HV: Fix KVM_RUN clobbering FP/VEC user registers

2023-11-29T11:24:21+00:00

Before running a guest, the host process (e.g., QEMU) FP/VEC registers
are saved if they were being used, similarly to when the kernel uses FP
registers. The guest values are then loaded into regs, and the host
process registers will be restored lazily when it uses FP/VEC.

KVM HV has a bug here: the host process registers do get saved, but the
user MSR bits remain enabled, which indicates the registers are valid
for the process. After they are clobbered by running the guest, this
valid indication causes the host process to take on the FP/VEC register
values of the guest.

Fixes: 34e119c96b2b ("KVM: PPC: Book3S HV P9: Reduce mtmsrd instructions required to save host SPRs")
Cc: stable@vger.kernel.org # v5.17+
Signed-off-by: Nicholas Piggin 
Signed-off-by: Michael Ellerman 
Link: https://msgid.link/20231122025811.2973-1-npiggin@gmail.com

powerpc: Hide empty pt_regs at base of the stack

2023-10-19T10:38:29+00:00

A thread started via eg. user_mode_thread() runs in the kernel to begin
with and then may later return to userspace. While it's running in the
kernel it has a pt_regs at the base of its kernel stack, but that
pt_regs is all zeroes.

If the thread oopses in that state, it leads to an ugly stack trace with
a big block of zero GPRs, as reported by Joel:

  Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)
  CPU: 0 PID: 1 Comm: swapper/0 Not tainted 6.5.0-rc7-00004-gf7757129e3de-dirty #3
  Hardware name: IBM PowerNV (emulated by qemu) POWER9 0x4e1200 opal:v7.0 PowerNV
  Call Trace:
  [c0000000036afb00] [c0000000010dd058] dump_stack_lvl+0x6c/0x9c (unreliable)
  [c0000000036afb30] [c00000000013c524] panic+0x178/0x424
  [c0000000036afbd0] [c000000002005100] mount_root_generic+0x250/0x324
  [c0000000036afca0] [c0000000020057d0] prepare_namespace+0x2d4/0x344
  [c0000000036afd20] [c0000000020049c0] kernel_init_freeable+0x358/0x3ac
  [c0000000036afdf0] [c0000000000111b0] kernel_init+0x30/0x1a0
  [c0000000036afe50] [c00000000000debc] ret_from_kernel_user_thread+0x14/0x1c
  --- interrupt: 0 at 0x0
  NIP:  0000000000000000 LR: 0000000000000000 CTR: 0000000000000000
  REGS: c0000000036afe80 TRAP: 0000   Not tainted  (6.5.0-rc7-00004-gf7757129e3de-dirty)
  MSR:  0000000000000000 <>  CR: 00000000  XER: 00000000
  CFAR: 0000000000000000 IRQMASK: 0
  GPR00: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
  GPR04: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
  GPR08: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
  GPR12: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
  GPR16: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
  GPR20: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
  GPR24: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
  GPR28: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
  NIP [0000000000000000] 0x0
  LR [0000000000000000] 0x0
  --- interrupt: 0

The all-zero pt_regs looks ugly and conveys no useful information, other
than its presence. So detect that case and just show the presence of the
frame by printing the interrupt marker, eg:

  Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)
  CPU: 0 PID: 1 Comm: swapper/0 Not tainted 6.5.0-rc3-00126-g18e9506562a0-dirty #301
  Hardware name: IBM pSeries (emulated by qemu) POWER9 (raw) 0x4e1202 0xf000005 of:SLOF,HEAD hv:linux,kvm pSeries
  Call Trace:
  [c000000003aabb00] [c000000001143db8] dump_stack_lvl+0x6c/0x9c (unreliable)
  [c000000003aabb30] [c00000000014c624] panic+0x178/0x424
  [c000000003aabbd0] [c0000000020050fc] mount_root_generic+0x250/0x324
  [c000000003aabca0] [c0000000020057cc] prepare_namespace+0x2d4/0x344
  [c000000003aabd20] [c0000000020049bc] kernel_init_freeable+0x358/0x3ac
  [c000000003aabdf0] [c0000000000111b0] kernel_init+0x30/0x1a0
  [c000000003aabe50] [c00000000000debc] ret_from_kernel_user_thread+0x14/0x1c
  --- interrupt: 0 at 0x0

To avoid ever suppressing a valid pt_regs make sure the pt_regs has a
zero MSR and TRAP value, and is located at the very base of the stack.

Fixes: 6895dfc04741 ("powerpc: copy_thread fill in interrupt frame marker and back chain")
Reported-by: Joel Stanley 
Reported-by: Nicholas Piggin 
Reviewed-by: Joel Stanley 
Signed-off-by: Michael Ellerman 
Link: https://msgid.link/20230824064210.907266-1-mpe@ellerman.id.au

powerpc/dexcr: Support userspace ROP protection

2023-06-19T07:36:26+00:00

The ISA 3.1B hashst and hashchk instructions use a per-cpu SPR HASHKEYR
to hold a key used in the hash calculation. This key should be different
for each process to make it harder for a malicious process to recreate
valid hash values for a victim process.

Add support for storing a per-thread hash key, and setting/clearing
HASHKEYR appropriately.

Signed-off-by: Benjamin Gray 
Reviewed-by: Russell Currey 
Signed-off-by: Michael Ellerman 
Link: https://msgid.link/20230616034846.311705-6-bgray@linux.ibm.com

powerpc: copy_thread don't set PPR in user interrupt frame regs

2023-04-11T13:13:33+00:00

syscalls do not set the PPR field in their interrupt frame and
return from syscall always sets the default PPR for userspace,
so setting the value in the ret_from_fork frame is not necessary
and mildly inconsistent. Remove it.

Signed-off-by: Nicholas Piggin 
Signed-off-by: Michael Ellerman 
Link: https://msgid.link/20230325122904.2375060-9-npiggin@gmail.com

powerpc: copy_thread don't set _TIF_RESTOREALL

2023-04-11T13:13:33+00:00

In the kernel user thread path, don't set _TIF_RESTOREALL because
the thread is required to call kernel_execve() before it returns,
which will set _TIF_RESTOREALL if necessary via start_thread().

Signed-off-by: Nicholas Piggin 
Signed-off-by: Michael Ellerman 
Link: https://msgid.link/20230325122904.2375060-8-npiggin@gmail.com

powerpc: differentiate kthread from user kernel thread start

2023-04-11T13:13:33+00:00

Kernel created user threads start similarly to kernel threads in that
they call a kernel function after first returning from _switch, so
they share ret_from_kernel_thread for this. Kernel threads never return
from that function though, whereas user threads often do (although some
don't, e.g., IO threads).

Split these startup functions in two, and catch kernel threads that
improperly return from their function. This is intended to make the
complicated code a little bit easier to understand.

Signed-off-by: Nicholas Piggin 
Signed-off-by: Michael Ellerman 
Link: https://msgid.link/20230325122904.2375060-7-npiggin@gmail.com

powerpc: copy_thread differentiate kthreads and user mode threads

2023-04-11T13:13:33+00:00

When copy_thread is given a kernel function to run in arg->fn, this
does not necessarily mean it is a kernel thread. User threads can be
created this way (e.g., kernel_init, see also x86's copy_thread()).
These threads run a kernel function which may call kernel_execve()
and return, which returns like a userspace exec(2) syscall.

Kernel threads are to  be differentiated with PF_KTHREAD, will always
have arg->fn set, and should never return from that function, instead
calling kthread_exit() to exit.

Create separate paths for the kthread and user kernel thread creation
logic. The kthread path will never exit and does not require a user
interrupt frame, so it gets a minimal stack frame.

Signed-off-by: Nicholas Piggin 
Signed-off-by: Michael Ellerman 
Link: https://msgid.link/20230325122904.2375060-6-npiggin@gmail.com