x86/entry: Fix AC assertion

The WARN added in commit 3c73b81 ("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: 3c73b81 ("x86/entry, selftests: Further improve user entry sanity checks") Signed-off-by: Peter Zijlstra (Intel) <[email protected]> Signed-off-by: Thomas Gleixner <[email protected]> Tested-by: Daniel Thompson <[email protected]> Acked-by: Andy Lutomirski <[email protected]> Cc: [email protected] Link: https://lore.kernel.org/r/[email protected]
antonovi · Sep 4, 2020 · 662a022 · 662a022
1 parent 2356bb4
commit 662a022
Showing 1 changed file with 10 additions and 2 deletions.
diff --git 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));