From 31ee977f709d28be1b62f47295e15cc464bab808 Mon Sep 17 00:00:00 2001 From: Mark Rutland Date: Thu, 24 Oct 2019 14:48:15 +0200 Subject: [PATCH] arm64: don't zero DIT on signal return [ Upstream commit 1265132127b63502d34e0f58c8bdef3a4dc927c2 ] Currently valid_user_regs() treats SPSR_ELx.DIT as a RES0 bit, causing it to be zeroed upon exception return, rather than preserved. Thus, code relying on DIT will not function as expected, and may expose an unexpected timing sidechannel. Let's remove DIT from the set of RES0 bits, such that it is preserved. At the same time, the related comment is updated to better describe the situation, and to take into account the most recent documentation of SPSR_ELx, in ARM DDI 0487C.a. Signed-off-by: Mark Rutland Fixes: 7206dc93a58fb764 ("arm64: Expose Arm v8.4 features") Cc: Catalin Marinas Cc: Suzuki K Poulose Cc: Will Deacon Signed-off-by: Will Deacon Signed-off-by: Ard Biesheuvel Signed-off-by: Greg Kroah-Hartman --- arch/arm64/kernel/ptrace.c | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-) diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c index 34d915b6974b..d8ff8f26db6d 100644 --- a/arch/arm64/kernel/ptrace.c +++ b/arch/arm64/kernel/ptrace.c @@ -1402,15 +1402,19 @@ asmlinkage void syscall_trace_exit(struct pt_regs *regs) } /* - * Bits which are always architecturally RES0 per ARM DDI 0487A.h + * SPSR_ELx bits which are always architecturally RES0 per ARM DDI 0487C.a + * We also take into account DIT (bit 24), which is not yet documented, and + * treat PAN and UAO as RES0 bits, as they are meaningless at EL0, and may be + * allocated an EL0 meaning in future. * Userspace cannot use these until they have an architectural meaning. + * Note that this follows the SPSR_ELx format, not the AArch32 PSR format. * We also reserve IL for the kernel; SS is handled dynamically. */ #define SPSR_EL1_AARCH64_RES0_BITS \ - (GENMASK_ULL(63,32) | GENMASK_ULL(27, 22) | GENMASK_ULL(20, 10) | \ - GENMASK_ULL(5, 5)) + (GENMASK_ULL(63,32) | GENMASK_ULL(27, 25) | GENMASK_ULL(23, 22) | \ + GENMASK_ULL(20, 10) | GENMASK_ULL(5, 5)) #define SPSR_EL1_AARCH32_RES0_BITS \ - (GENMASK_ULL(63,32) | GENMASK_ULL(24, 22) | GENMASK_ULL(20,20)) + (GENMASK_ULL(63,32) | GENMASK_ULL(23, 22) | GENMASK_ULL(20,20)) static int valid_compat_regs(struct user_pt_regs *regs) { -- 2.20.1