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| author | Joey Gouly <joey.gouly@arm.com> | 2022-04-05 13:47:33 +0300 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2022-04-20 10:34:16 +0300 |
| commit | ed2711c696ceb0bad5259bf338044c8a589c798d (patch) | |
| tree | 123da4cefd2771df463845fd46825b8211d4fec2 /arch | |
| parent | cfd24b14eb2d435d4555e9bc15d68d50bd21c105 (diff) | |
| download | linux-ed2711c696ceb0bad5259bf338044c8a589c798d.tar.xz | |
arm64: alternatives: mark patch_alternative() as `noinstr`
[ Upstream commit a2c0b0fbe01419f8f5d1c0b9c581631f34ffce8b ]
The alternatives code must be `noinstr` such that it does not patch itself,
as the cache invalidation is only performed after all the alternatives have
been applied.
Mark patch_alternative() as `noinstr`. Mark branch_insn_requires_update()
and get_alt_insn() with `__always_inline` since they are both only called
through patch_alternative().
Booting a kernel in QEMU TCG with KCSAN=y and ARM64_USE_LSE_ATOMICS=y caused
a boot hang:
[ 0.241121] CPU: All CPU(s) started at EL2
The alternatives code was patching the atomics in __tsan_read4() from LL/SC
atomics to LSE atomics.
The following fragment is using LL/SC atomics in the .text section:
| <__tsan_unaligned_read4+304>: ldxr x6, [x2]
| <__tsan_unaligned_read4+308>: add x6, x6, x5
| <__tsan_unaligned_read4+312>: stxr w7, x6, [x2]
| <__tsan_unaligned_read4+316>: cbnz w7, <__tsan_unaligned_read4+304>
This LL/SC atomic sequence was to be replaced with LSE atomics. However since
the alternatives code was instrumentable, __tsan_read4() was being called after
only the first instruction was replaced, which led to the following code in memory:
| <__tsan_unaligned_read4+304>: ldadd x5, x6, [x2]
| <__tsan_unaligned_read4+308>: add x6, x6, x5
| <__tsan_unaligned_read4+312>: stxr w7, x6, [x2]
| <__tsan_unaligned_read4+316>: cbnz w7, <__tsan_unaligned_read4+304>
This caused an infinite loop as the `stxr` instruction never completed successfully,
so `w7` was always 0.
Signed-off-by: Joey Gouly <joey.gouly@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20220405104733.11476-1-joey.gouly@arm.com
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Diffstat (limited to 'arch')
| -rw-r--r-- | arch/arm64/kernel/alternative.c | 6 |
1 files changed, 3 insertions, 3 deletions
diff --git a/arch/arm64/kernel/alternative.c b/arch/arm64/kernel/alternative.c index 3fb79b76e9d9..7bbf5104b7b7 100644 --- a/arch/arm64/kernel/alternative.c +++ b/arch/arm64/kernel/alternative.c @@ -42,7 +42,7 @@ bool alternative_is_applied(u16 cpufeature) /* * Check if the target PC is within an alternative block. */ -static bool branch_insn_requires_update(struct alt_instr *alt, unsigned long pc) +static __always_inline bool branch_insn_requires_update(struct alt_instr *alt, unsigned long pc) { unsigned long replptr = (unsigned long)ALT_REPL_PTR(alt); return !(pc >= replptr && pc <= (replptr + alt->alt_len)); @@ -50,7 +50,7 @@ static bool branch_insn_requires_update(struct alt_instr *alt, unsigned long pc) #define align_down(x, a) ((unsigned long)(x) & ~(((unsigned long)(a)) - 1)) -static u32 get_alt_insn(struct alt_instr *alt, __le32 *insnptr, __le32 *altinsnptr) +static __always_inline u32 get_alt_insn(struct alt_instr *alt, __le32 *insnptr, __le32 *altinsnptr) { u32 insn; @@ -95,7 +95,7 @@ static u32 get_alt_insn(struct alt_instr *alt, __le32 *insnptr, __le32 *altinsnp return insn; } -static void patch_alternative(struct alt_instr *alt, +static noinstr void patch_alternative(struct alt_instr *alt, __le32 *origptr, __le32 *updptr, int nr_inst) { __le32 *replptr; |