From: Will Deacon will@kernel.org
[ Upstream commit 893b24181b4c4bf1fa2841b1ed192e5413a97cb1 ]
The FFR is a predicate register which can vary between 16 and 256 bits in size depending upon the configured vector length. When saving the SVE state in streaming SVE mode, the FFR register is inaccessible and so commit 9f5848665788 ("arm64/sve: Make access to FFR optional") simply clears the FFR field of the in-memory context structure. Unfortunately, it achieves this using an unconditional 8-byte store and so if the SME vector length is anything other than 64 bytes in size we will either fail to clear the entire field or, worse, we will corrupt memory immediately following the structure. This has led to intermittent kfence splats in CI [1] and can trigger kmalloc Redzone corruption messages when running the 'fp-stress' kselftest:
| ============================================================================= | BUG kmalloc-1k (Not tainted): kmalloc Redzone overwritten | ----------------------------------------------------------------------------- | | 0xffff000809bf1e22-0xffff000809bf1e27 @offset=7714. First byte 0x0 instead of 0xcc | Allocated in do_sme_acc+0x9c/0x220 age=2613 cpu=1 pid=531 | __kmalloc+0x8c/0xcc | do_sme_acc+0x9c/0x220 | ...
Replace the 8-byte store with a store of a predicate register which has been zero-initialised with PFALSE, ensuring that the entire field is cleared in memory.
[1] https://lore.kernel.org/r/CA+G9fYtU7HsV0R0dp4XEH5xXHSJFw8KyDf5VQrLLfMxWfxQka...
Cc: Mark Brown broonie@kernel.org Cc: Mark Rutland mark.rutland@arm.com Cc: Naresh Kamboju naresh.kamboju@linaro.org Fixes: 9f5848665788 ("arm64/sve: Make access to FFR optional") Reported-by: Linux Kernel Functional Testing lkft@linaro.org Signed-off-by: Will Deacon will@kernel.org Reviewed-by: Mark Brown broonie@kernel.org Tested-by: Anders Roxell anders.roxell@linaro.org Link: https://lore.kernel.org/r/20230628155605.22296-1-will@kernel.org Signed-off-by: Catalin Marinas catalin.marinas@arm.com Signed-off-by: Sasha Levin sashal@kernel.org --- arch/arm64/include/asm/fpsimdmacros.h | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/arch/arm64/include/asm/fpsimdmacros.h b/arch/arm64/include/asm/fpsimdmacros.h index cd03819a3b686..cdf6a35e39944 100644 --- a/arch/arm64/include/asm/fpsimdmacros.h +++ b/arch/arm64/include/asm/fpsimdmacros.h @@ -316,12 +316,12 @@ _for n, 0, 15, _sve_str_p \n, \nxbase, \n - 16 cbz \save_ffr, 921f _sve_rdffr 0 - _sve_str_p 0, \nxbase - _sve_ldr_p 0, \nxbase, -16 b 922f 921: - str xzr, [x\nxbase] // Zero out FFR + _sve_pfalse 0 // Zero out FFR 922: + _sve_str_p 0, \nxbase + _sve_ldr_p 0, \nxbase, -16 mrs x\nxtmp, fpsr str w\nxtmp, [\xpfpsr] mrs x\nxtmp, fpcr