x86/kprobes: Fix crash when probing CS CALL instructionsgrafted

When using eBPF to probe CS CALL instructions within a function,
a crash can be triggered.

The eBPF tool probes offset 257 of the __hrtimer_run_queues()
function:

<__hrtimer_run_queues+249>:  nopl   0x0(%rax,%rax,1)
<__hrtimer_run_queues+254>:  mov    %r14,%rdi
<__hrtimer_run_queues+257>:  cs call <__x86_indirect_thunk_r12>
<__hrtimer_run_queues+263>:  mov    %eax,%r12d
<__hrtimer_run_queues+266>:  xchg   %ax,%ax
<__hrtimer_run_queues+268>:  mov    %r13,%rdi

Which triggers this crash:

  BUG: unable to handle page fault for address: 00000000000f41c9
  #PF: supervisor write access in kernel mode
  #PF: error_code(0x0002) - not-present page
  PGD 0 P4D 0
  Oops: 0002 [#1] SMP NOPTI
  CPU: 1 PID: 0 Comm: swapper/1 Kdump: loaded Tainted: P
  RIP: 0010:__hrtimer_run_queues+0x106/0x230

Note that __hrtimer_run_queues+0x106 is __hrtimer_run_queues+262, which is
at the 6th byte of the above CS CALL instruction. Since the CS CALL
instruction occupies 6 bytes, the exception occurred in the middle of that
call instruction.

The root cause is that when using eBPF tools to probe in the middle of a
function, a kprobe with INT3 is used as the underlying implementation.

During single-step emulation of the original CALL instruction,
int3_emulate_call() assumes that the probed CALL instruction is 5 bytes
long. However, the actual CS-prefixed CALL instruction occupies 6 bytes,
so it constructs an incorrect exception return address. When the CPU
returns from the kprobe handler, the next instruction to be executed is at
the address of the last byte of that CS CALL instruction. Coincidentally,
starting from that address, the CPU fetches and decodes a completely
different instruction, which ultimately triggers a kernel crash.

Fix the issue by using the actual instruction length obtained from
the instruction decoder when constructing the exception return
address, rather than relying on the hardcoded CALL_INSN_SIZE macro.

[ mingo: Refined the changelog ]

Fixes: 6256e668b7af ("x86/kprobes: Use int3 instead of debug trap for single-step")
Suggested-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Jinke Han <jinkehan@didiglobal.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Acked-by: Yafang Shao <laoar.shao@gmail.com>
Acked-by: Borislav Petkov <bp@alien8.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://patch.msgid.link/20260908073742.GA10517@didi-ThinkCentre-M920t-N000

1 files changed, 33 insertions, 0 deletions

diff --git a/Documentation/gpu/amdgpu/flashing.rst b/Documentation/gpu/amdgpu/flashing.rst
new file mode 100644
index 000000000..bd745c42a
--- /dev/null
+++ b/Documentation/gpu/amdgpu/flashing.rst
@@ -0,0 +1,33 @@
+=======================
+ dGPU firmware flashing
+=======================
+
+IFWI
+----
+Flashing the dGPU integrated firmware image (IFWI) is supported by GPUs that
+use the PSP to orchestrate the update (Navi3x or newer GPUs).
+For supported GPUs, `amdgpu` will export a series of sysfs files that can be
+used for the flash process.
+
+The IFWI flash process is:
+
+1. Ensure the IFWI image is intended for the dGPU on the system.
+2. "Write" the IFWI image to the sysfs file `psp_vbflash`. This will stage the IFWI in memory.
+3. "Read" from the `psp_vbflash` sysfs file to initiate the flash process.
+4. Poll the `psp_vbflash_status` sysfs file to determine when the flash process completes.
+
+USB-C PD F/W
+------------
+On GPUs that support flashing an updated USB-C PD firmware image, the process
+is done using the `usbc_pd_fw` sysfs file.
+
+* Reading the file will provide the current firmware version.
+* Writing the name of a firmware payload stored in `/lib/firmware/amdgpu` to the sysfs file will initiate the flash process.
+
+The firmware payload stored in `/lib/firmware/amdgpu` can be named any name
+as long as it doesn't conflict with other existing binaries that are used by
+`amdgpu`.
+
+sysfs files
+-----------
+.. kernel-doc:: drivers/gpu/drm/amd/amdgpu/amdgpu_psp.c