From 893b24181b4c4bf1fa2841b1ed192e5413a97cb1 Mon Sep 17 00:00:00 2001 From: Will Deacon Date: Wed, 28 Jun 2023 16:56:05 +0100 Subject: [PATCH] arm64: sme: Use STR P to clear FFR context field in streaming SVE mode 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+G9fYtU7HsV0R0dp4XEH5xXHSJFw8KyDf5VQrLLfMxWfxQkag@mail.gmail.com Cc: Mark Brown Cc: Mark Rutland Cc: Naresh Kamboju Fixes: 9f5848665788 ("arm64/sve: Make access to FFR optional") Reported-by: Linux Kernel Functional Testing Signed-off-by: Will Deacon Reviewed-by: Mark Brown Tested-by: Anders Roxell Link: https://lore.kernel.org/r/20230628155605.22296-1-will@kernel.org Signed-off-by: Catalin Marinas --- 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 cd03819a3b68..cdf6a35e3994 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