9ddfc3cd80
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: ebc00dde8a ("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>
63 lines
1.4 KiB
C
63 lines
1.4 KiB
C
/* SPDX-License-Identifier: GPL-2.0-only */
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/*
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* Copyright (C) 2020 Emil Renner Berthing
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*
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* Based on arch/arm64/include/asm/jump_label.h
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*/
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#ifndef __ASM_JUMP_LABEL_H
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#define __ASM_JUMP_LABEL_H
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#ifndef __ASSEMBLY__
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#include <linux/types.h>
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#include <asm/asm.h>
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#define JUMP_LABEL_NOP_SIZE 4
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static __always_inline bool arch_static_branch(struct static_key * const key,
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const bool branch)
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{
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asm_volatile_goto(
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" .align 2 \n\t"
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" .option push \n\t"
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" .option norelax \n\t"
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" .option norvc \n\t"
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"1: nop \n\t"
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" .option pop \n\t"
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" .pushsection __jump_table, \"aw\" \n\t"
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" .align " RISCV_LGPTR " \n\t"
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" .long 1b - ., %l[label] - . \n\t"
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" " RISCV_PTR " %0 - . \n\t"
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" .popsection \n\t"
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: : "i"(&((char *)key)[branch]) : : label);
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return false;
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label:
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return true;
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}
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static __always_inline bool arch_static_branch_jump(struct static_key * const key,
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const bool branch)
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{
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asm_volatile_goto(
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" .align 2 \n\t"
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" .option push \n\t"
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" .option norelax \n\t"
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" .option norvc \n\t"
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"1: jal zero, %l[label] \n\t"
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" .option pop \n\t"
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" .pushsection __jump_table, \"aw\" \n\t"
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" .align " RISCV_LGPTR " \n\t"
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" .long 1b - ., %l[label] - . \n\t"
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" " RISCV_PTR " %0 - . \n\t"
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" .popsection \n\t"
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: : "i"(&((char *)key)[branch]) : : label);
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return false;
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label:
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return true;
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}
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#endif /* __ASSEMBLY__ */
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#endif /* __ASM_JUMP_LABEL_H */
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