The following commit has been merged into the x86/urgent branch of tip:

Commit-ID: 662a0221893a3d58aa72719671844264306f6e4b Gitweb: https://git.kernel.org/tip/662a0221893a3d58aa72719671844264306f6e4b Author: Peter Zijlstra peterz@infradead.org AuthorDate: Wed, 02 Sep 2020 15:25:50 +02:00 Committer: Thomas Gleixner tglx@linutronix.de CommitterDate: Fri, 04 Sep 2020 15:09:29 +02:00

x86/entry: Fix AC assertion

The WARN added in commit 3c73b81a9164 ("x86/entry, selftests: Further improve user entry sanity checks") unconditionally triggers on a IVB machine because it does not support SMAP.

For !SMAP hardware the CLAC/STAC instructions are patched out and thus if userspace sets AC, it is still have set after entry.

Fixes: 3c73b81a9164 ("x86/entry, selftests: Further improve user entry sanity checks") Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Signed-off-by: Thomas Gleixner tglx@linutronix.de Tested-by: Daniel Thompson daniel.thompson@linaro.org Acked-by: Andy Lutomirski luto@kernel.org Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/20200902133200.666781610@infradead.org

--- arch/x86/include/asm/entry-common.h | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/entry-common.h b/arch/x86/include/asm/entry-common.h index a8f9315..6fe54b2 100644 --- a/arch/x86/include/asm/entry-common.h +++ b/arch/x86/include/asm/entry-common.h @@ -18,8 +18,16 @@ static __always_inline void arch_check_user_regs(struct pt_regs *regs) * state, not the interrupt state as imagined by Xen. */ unsigned long flags = native_save_fl(); - WARN_ON_ONCE(flags & (X86_EFLAGS_AC | X86_EFLAGS_DF | - X86_EFLAGS_NT)); + unsigned long mask = X86_EFLAGS_DF | X86_EFLAGS_NT; + + /* + * For !SMAP hardware we patch out CLAC on entry. + */ + if (boot_cpu_has(X86_FEATURE_SMAP) || + (IS_ENABLED(CONFIG_64_BIT) && boot_cpu_has(X86_FEATURE_XENPV))) + mask |= X86_EFLAGS_AC; + + WARN_ON_ONCE(flags & mask);

/* We think we came from user mode. Make sure pt_regs agrees. */ WARN_ON_ONCE(!user_mode(regs));