diff options
| author | Guo Ren <guoren@linux.alibaba.com> | 2023-01-12 04:05:59 -0500 |
|---|---|---|
| committer | Palmer Dabbelt <palmer@rivosinc.com> | 2023-02-15 10:58:21 -0800 |
| commit | 6724a76cff85ee271bbbff42ac527e4643b2ec52 (patch) | |
| tree | 898687ed78031762b00fc08163d66dbf72bb3a38 /arch/riscv/Makefile | |
| parent | 409c8fb20c66df7150e592747412438c04aeb11f (diff) | |
riscv: ftrace: Reduce the detour code size to half
Use a temporary register to reduce the size of detour code from 16 bytes to
8 bytes. The previous implementation is from 'commit afc76b8b8011 ("riscv:
Using PATCHABLE_FUNCTION_ENTRY instead of MCOUNT")'.
Before the patch:
<func_prolog>:
0: REG_S ra, -SZREG(sp)
4: auipc ra, ?
8: jalr ?(ra)
12: REG_L ra, -SZREG(sp)
(func_boddy)
After the patch:
<func_prolog>:
0: auipc t0, ?
4: jalr t0, ?(t0)
(func_boddy)
This patch not just reduces the size of detour code, but also fixes an
important issue:
An Ftrace callback registered with FTRACE_OPS_FL_IPMODIFY flag can
actually change the instruction pointer, e.g. to "replace" the given
kernel function with a new one, which is needed for livepatching, etc.
In this case, the trampoline (ftrace_regs_caller) would not return to
<func_prolog+12> but would rather jump to the new function. So, "REG_L
ra, -SZREG(sp)" would not run and the original return address would not
be restored. The kernel is likely to hang or crash as a result.
This can be easily demonstrated if one tries to "replace", say,
cmdline_proc_show() with a new function with the same signature using
instruction_pointer_set(&fregs->regs, new_func_addr) in the Ftrace
callback.
Link: https://lore.kernel.org/linux-riscv/20221122075440.1165172-1-suagrfillet@gmail.com/
Link: https://lore.kernel.org/linux-riscv/d7d5730b-ebef-68e5-5046-e763e1ee6164@yadro.com/
Co-developed-by: Song Shuai <suagrfillet@gmail.com>
Signed-off-by: Song Shuai <suagrfillet@gmail.com>
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Signed-off-by: Guo Ren <guoren@kernel.org>
Cc: Evgenii Shatokhin <e.shatokhin@yadro.com>
Reviewed-by: Evgenii Shatokhin <e.shatokhin@yadro.com>
Link: https://lore.kernel.org/r/20230112090603.1295340-4-guoren@kernel.org
Cc: stable@vger.kernel.org
Fixes: 10626c32e382 ("riscv/ftrace: Add basic support")
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
Diffstat (limited to 'arch/riscv/Makefile')
| -rw-r--r-- | arch/riscv/Makefile | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile index e194916cb5a2..ab50724cc554 100644 --- a/arch/riscv/Makefile +++ b/arch/riscv/Makefile @@ -12,9 +12,9 @@ ifeq ($(CONFIG_DYNAMIC_FTRACE),y) LDFLAGS_vmlinux := --no-relax KBUILD_CPPFLAGS += -DCC_USING_PATCHABLE_FUNCTION_ENTRY ifeq ($(CONFIG_RISCV_ISA_C),y) - CC_FLAGS_FTRACE := -fpatchable-function-entry=8 -else CC_FLAGS_FTRACE := -fpatchable-function-entry=4 +else + CC_FLAGS_FTRACE := -fpatchable-function-entry=2 endif endif |