diff options
| author | Andy Chiu | 2023-02-06 04:04:40 -0500 |
|---|---|---|
| committer | Palmer Dabbelt | 2023-02-21 17:21:16 -0800 |
| commit | 9ddfc3cd806081ce1f6c9c2f988cbb031f35d28f (patch) | |
| tree | 1a144af3e446d6a03d43f56190fca3e929013904 /arch/riscv | |
| parent | 2350bd192fa2d9ffa7a0dc7db12699c0f71af7f8 (diff) | |
riscv: jump_label: Fixup unaligned arch_static_branch function
Runtime code patching must be done at a naturally aligned address, or we
may execute on a partial instruction.
We have encountered problems traced back to static jump functions during
the test. We switched the tracer randomly for every 1~5 seconds on a
dual-core QEMU setup and found the kernel sucking at a static branch
where it jumps to itself.
The reason is that the static branch was 2-byte but not 4-byte aligned.
Then, the kernel would patch the instruction, either J or NOP, with two
half-word stores if the machine does not have efficient unaligned
accesses. Thus, moments exist where half of the NOP mixes with the other
half of the J when transitioning the branch. In our particular case, on
a little-endian machine, the upper half of the NOP was mixed with the
lower part of the J when enabling the branch, resulting in a jump that
jumped to itself. Conversely, it would result in a HINT instruction when
disabling the branch, but it might not be observable.
ARM64 does not have this problem since all instructions must be 4-byte
aligned.
Fixes: ebc00dde8a97 ("riscv: Add jump-label implementation")
Link: https://lore.kernel.org/linux-riscv/20220913094252.3555240-6-andy.chiu@sifive.com/
Reviewed-by: Greentime Hu <greentime.hu@sifive.com>
Signed-off-by: Andy Chiu <andy.chiu@sifive.com>
Signed-off-by: Guo Ren <guoren@kernel.org>
Link: https://lore.kernel.org/r/20230206090440.1255001-1-guoren@kernel.org
Cc: stable@vger.kernel.org
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
Diffstat (limited to 'arch/riscv')
| -rw-r--r-- | arch/riscv/include/asm/jump_label.h | 2 |
1 files changed, 2 insertions, 0 deletions
diff --git a/arch/riscv/include/asm/jump_label.h b/arch/riscv/include/asm/jump_label.h index 6d58bbb5da46..14a5ea8d8ef0 100644 --- a/arch/riscv/include/asm/jump_label.h +++ b/arch/riscv/include/asm/jump_label.h @@ -18,6 +18,7 @@ static __always_inline bool arch_static_branch(struct static_key * const key, const bool branch) { asm_volatile_goto( + " .align 2 \n\t" " .option push \n\t" " .option norelax \n\t" " .option norvc \n\t" @@ -39,6 +40,7 @@ static __always_inline bool arch_static_branch_jump(struct static_key * const ke const bool branch) { asm_volatile_goto( + " .align 2 \n\t" " .option push \n\t" " .option norelax \n\t" " .option norvc \n\t" |