From 925778f7d1ca00cea3dabb405b7c8834be2a771b Mon Sep 17 00:00:00 2001 From: Keir Fraser Date: Tue, 25 Mar 2025 14:09:33 +0000 Subject: [PATCH] FROMLIST: arm64: mops: Do not dereference src reg for a set operation The source register is not used for SET* and reading it can result in a UBSAN out-of-bounds array access error, specifically when the MOPS exception is taken from a SET* sequence with XZR (reg 31) as the source. Architecturally this is the only case where a src/dst/size field in the ESR can be reported as 31. Prior to 2de451a329cf662b the code in do_el0_mops() was benign as the use of pt_regs_read_reg() prevented the out-of-bounds access. Fixes: 2de451a329cf662b ("KVM: arm64: Add handler for MOPS exceptions") Bug: 406015947 Link: https://lore.kernel.org/all/20250326110059.3773318-1-keirf@google.com/ Change-Id: I7e5e195f48b2968310a11fcb314fb7717738bd06 Reviewed-by: Marc Zyngier Acked-by: Mark Rutland Signed-off-by: Keir Fraser --- arch/arm64/include/asm/traps.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/arch/arm64/include/asm/traps.h b/arch/arm64/include/asm/traps.h index d780d1bd2eac..82cf1f879c61 100644 --- a/arch/arm64/include/asm/traps.h +++ b/arch/arm64/include/asm/traps.h @@ -109,10 +109,9 @@ static inline void arm64_mops_reset_regs(struct user_pt_regs *regs, unsigned lon int dstreg = ESR_ELx_MOPS_ISS_DESTREG(esr); int srcreg = ESR_ELx_MOPS_ISS_SRCREG(esr); int sizereg = ESR_ELx_MOPS_ISS_SIZEREG(esr); - unsigned long dst, src, size; + unsigned long dst, size; dst = regs->regs[dstreg]; - src = regs->regs[srcreg]; size = regs->regs[sizereg]; /* @@ -129,6 +128,7 @@ static inline void arm64_mops_reset_regs(struct user_pt_regs *regs, unsigned lon } } else { /* CPY* instruction */ + unsigned long src = regs->regs[srcreg]; if (!(option_a ^ wrong_option)) { /* Format is from Option B */ if (regs->pstate & PSR_N_BIT) {