From: Peter Zijlstra <[email protected]>
The WARN added in commit 3c73b81a9164 ("x86/entry, selftests: Further
improve user entry sanity checks") unconditionally triggers on my IVB
machine because it does not support SMAP.
For !SMAP hardware we patch out CLAC/STAC instructions and thus if
userspace sets AC, we'll still have it set after entry.
Fixes: 3c73b81a9164 ("x86/entry, selftests: Further improve user entry sanity
checks")
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Acked-by: Andy Lutomirski <[email protected]>
---
arch/x86/include/asm/entry-common.h | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)
--- 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_u
* 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));
