From: Mark Rutland mark.rutland@arm.com
[ 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 mark.rutland@arm.com Fixes: 7206dc93a58fb764 ("arm64: Expose Arm v8.4 features") Cc: Catalin Marinas catalin.marinas@arm.com Cc: Suzuki K Poulose suzuki.poulose@arm.com Cc: Will Deacon will.deacon@arm.com Signed-off-by: Will Deacon will.deacon@arm.com Signed-off-by: Ard Biesheuvel ard.biesheuvel@linaro.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/arm64/kernel/ptrace.c | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-)
--- a/arch/arm64/kernel/ptrace.c +++ b/arch/arm64/kernel/ptrace.c @@ -1402,15 +1402,19 @@ asmlinkage void syscall_trace_exit(struc }
/* - * 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) {