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, 66 insertions, 0 deletions

diff --git a/Documentation/fb/pvr2fb.rst b/Documentation/fb/pvr2fb.rst
new file mode 100644
index 000000000..315ce085a
--- /dev/null
+++ b/Documentation/fb/pvr2fb.rst
@@ -0,0 +1,66 @@
+===============================================
+pvr2fb - PowerVR 2 graphics frame buffer driver
+===============================================
+
+This is a driver for PowerVR 2 based graphics frame buffers, such as the
+one found in the Dreamcast.
+
+Advantages:
+
+ * It provides a nice large console (128 cols + 48 lines with 1024x768)
+   without using tiny, unreadable fonts (NOT on the Dreamcast)
+ * You can run XF86_FBDev on top of /dev/fb0
+ * Most important: boot logo :-)
+
+Disadvantages:
+
+ * Driver is largely untested on non-Dreamcast systems.
+
+Configuration
+=============
+
+You can pass kernel command line options to pvr2fb with
+`video=pvr2fb:option1,option2:value2,option3` (multiple options should be
+separated by comma, values are separated from options by `:`).
+
+Accepted options:
+
+==========  ==================================================================
+font:X      default font to use. All fonts are supported, including the
+	    SUN12x22 font which is very nice at high resolutions.
+
+
+mode:X      default video mode with format [xres]x[yres]-<bpp>@<refresh rate>
+	    The following video modes are supported:
+	    640x640-16@60, 640x480-24@60, 640x480-32@60. The Dreamcast
+	    defaults to 640x480-16@60. At the time of writing the
+	    24bpp and 32bpp modes function poorly. Work to fix that is
+	    ongoing
+
+	    Note: the 640x240 mode is currently broken, and should not be
+	    used for any reason. It is only mentioned here as a reference.
+
+inverse     invert colors on screen (for LCD displays)
+
+nomtrr      disables write combining on frame buffer. This slows down driver
+	    but there is reported minor incompatibility between GUS DMA and
+	    XFree under high loads if write combining is enabled (sound
+	    dropouts). MTRR is enabled by default on systems that have it
+	    configured and that support it.
+
+cable:X     cable type. This can be any of the following: vga, rgb, and
+	    composite. If none is specified, we guess.
+
+output:X    output type. This can be any of the following: pal, ntsc, and
+	    vga. If none is specified, we guess.
+==========  ==================================================================
+
+X11
+===
+
+XF86_FBDev has been shown to work on the Dreamcast in the past - though not yet
+on any 2.6 series kernel.
+
+Paul Mundt <lethal@linuxdc.org>
+
+Updated by Adrian McMenamin <adrian@mcmen.demon.co.uk>