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, 187 insertions, 0 deletions

diff --git a/Documentation/dev-tools/propeller.rst b/Documentation/dev-tools/propeller.rst
new file mode 100644
index 000000000..e92731994
--- /dev/null
+++ b/Documentation/dev-tools/propeller.rst
@@ -0,0 +1,187 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+=====================================
+Using Propeller with the Linux kernel
+=====================================
+
+This enables Propeller build support for the kernel when using Clang
+compiler. Propeller is a profile-guided optimization (PGO) method used
+to optimize binary executables. Like AutoFDO, it utilizes hardware
+sampling to gather information about the frequency of execution of
+different code paths within a binary. Unlike AutoFDO, this information
+is then used right before linking phase to optimize (among others)
+block layout within and across functions.
+
+A few important notes about adopting Propeller optimization:
+
+#. Although it can be used as a standalone optimization step, it is
+   strongly recommended to apply Propeller on top of AutoFDO,
+   AutoFDO+ThinLTO or Instrument FDO. The rest of this document
+   assumes this paradigm.
+
+#. Propeller uses another round of profiling on top of
+   AutoFDO/AutoFDO+ThinLTO/iFDO. The whole build process involves
+   "build-afdo - train-afdo - build-propeller - train-propeller -
+   build-optimized".
+
+#. Propeller requires LLVM 19 release or later for Clang/Clang++
+   and the linker(ld.lld).
+
+#. In addition to LLVM toolchain, Propeller requires a profiling
+   conversion tool: https://github.com/google/llvm-propeller.
+
+Current supported architectures include x86/X86_64 (via LBR),
+and arm64 (via SPE).
+
+The Propeller optimization process involves the following steps:
+
+#. Initial building: Build the AutoFDO or AutoFDO+ThinLTO binary as
+   you would normally do, but with a set of compile-time / link-time
+   flags, so that a special metadata section is created within the
+   kernel binary. The special section is only intend to be used by the
+   profiling tool, it is not part of the runtime image, nor does it
+   change kernel run time text sections.
+
+#. Profiling: The above kernel is then run with a representative
+   workload to gather execution frequency data. This data is collected
+   using hardware sampling, via perf. Propeller is most effective on
+   platforms supporting advanced PMU features like LBR on Intel
+   machines. This step is the same as profiling the kernel for AutoFDO
+   (the exact perf parameters can be different).
+
+#. Propeller profile generation: Perf output file is converted to a
+   pair of Propeller profiles via an offline tool.
+
+#. Optimized build: Build the AutoFDO or AutoFDO+ThinLTO optimized
+   binary as you would normally do, but with a compile-time /
+   link-time flag to pick up the Propeller compile time and link time
+   profiles. This build step uses 3 profiles - the AutoFDO profile,
+   the Propeller compile-time profile and the Propeller link-time
+   profile.
+
+#. Deployment: The optimized kernel binary is deployed and used
+   in production environments, providing improved performance
+   and reduced latency.
+
+Preparation
+===========
+
+Configure the kernel with::
+
+   CONFIG_AUTOFDO_CLANG=y
+   CONFIG_PROPELLER_CLANG=y
+
+Customization
+=============
+
+The default CONFIG_PROPELLER_CLANG setting covers kernel space objects
+for Propeller builds. One can, however, enable or disable Propeller build
+for individual files and directories by adding a line similar to the
+following to the respective kernel Makefile:
+
+- For enabling a single file (e.g. foo.o)::
+
+   PROPELLER_PROFILE_foo.o := y
+
+- For enabling all files in one directory::
+
+   PROPELLER_PROFILE := y
+
+- For disabling one file::
+
+   PROPELLER_PROFILE_foo.o := n
+
+- For disabling all files in one directory::
+
+   PROPELLER__PROFILE := n
+
+
+Workflow
+========
+
+Here is an example workflow for building an AutoFDO+Propeller kernel:
+
+1) Assuming an AutoFDO profile is already collected following
+   instructions in the AutoFDO document, build the kernel on the host
+   machine, with AutoFDO and Propeller build configs ::
+
+      CONFIG_AUTOFDO_CLANG=y
+      CONFIG_PROPELLER_CLANG=y
+
+   and ::
+
+      $ make LLVM=1 CLANG_AUTOFDO_PROFILE=<autofdo-profile-name>
+
+2) Install the kernel on the test machine.
+
+3) Run the load tests. The '-c' option in perf specifies the sample
+   event period. We suggest using a suitable prime number, like 500009,
+   for this purpose.
+
+   - For Intel platforms::
+
+      $ perf record -e BR_INST_RETIRED.NEAR_TAKEN:k -a -N -b -c <count> -o <perf_file> -- <loadtest>
+
+   - For AMD platforms::
+
+      $ perf record --pfm-event RETIRED_TAKEN_BRANCH_INSTRUCTIONS:k -a -N -b -c <count> -o <perf_file> -- <loadtest>
+
+   - For arm64 with SPE::
+     There are a few kernel features that must be enabled to collect SPE profiles on Arm.
+     Below is a list of the required features:
+
+      - CONFIG_ARM_SPE_PMU=y
+      - CONFIG_PID_IN_CONTEXTIDR=y
+      - kpti=off
+
+     Use the following command to generate SPE perf data file::
+
+      $ perf record -e 'arm_spe_0/branch_filter=1,load_filter=0,store_filter=0/' -a -N -c <count> --no-switch-events -o <perf_file> -- <loadtest>
+
+     Note you can repeat the above steps to collect multiple <perf_file>s.
+
+4) (Optional) Download the raw perf file(s) to the host machine.
+
+5) Use the generate_propeller_profiles tool (https://github.com/google/llvm-propeller) to
+   generate Propeller profile. ::
+
+      $ generate_propeller_profiles \
+             --binary=<vmlinux> --profile=<perf_file> \
+             --format=propeller --propeller_output_module_name \
+             --out=<propeller_profile_prefix>_cc_profile.txt \
+             --propeller_symorder=<propeller_profile_prefix>_ld_profile.txt
+
+   "<propeller_profile_prefix>" can be something like "/home/user/dir/any_string".
+
+   This command generates a pair of Propeller profiles:
+   "<propeller_profile_prefix>_cc_profile.txt" and
+   "<propeller_profile_prefix>_ld_profile.txt".
+
+   If there are more than 1 perf_file collected in the previous step,
+   you can create a temp list file "<perf_file_list>" with each line
+   containing one perf file name and run::
+
+      $ generate_propeller_profiles \
+             --binary=<vmlinux> --profile=@<perf_file_list> \
+             --format=propeller --propeller_output_module_name \
+             --out=<propeller_profile_prefix>_cc_profile.txt \
+             --propeller_symorder=<propeller_profile_prefix>_ld_profile.txt
+
+   For arm64 SPE, add the option '--profiler=perf_spe', like::
+
+      $ generate_propeller_profiles  \
+             --binary=<vmlinux> --profile=<perf_file> \
+             --profiler=perf_spe \
+             --format=propeller --propeller_output_module_name \
+             --out=<propeller_profile_prefix>_cc_profile.txt \
+             --propeller_symorder=<propeller_profile_prefix>_ld_profile.txt
+
+6) Rebuild the kernel using the AutoFDO and Propeller
+   profiles. ::
+
+      CONFIG_AUTOFDO_CLANG=y
+      CONFIG_PROPELLER_CLANG=y
+
+   and ::
+
+      $ make LLVM=1 CLANG_AUTOFDO_PROFILE=<profile_file> CLANG_PROPELLER_PROFILE_PREFIX=<propeller_profile_prefix>