From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
commit 662a0221893a3d58aa72719671844264306f6e4b upstream.
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@xxxxxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Tested-by: Daniel Thompson <daniel.thompson@xxxxxxxxxx>
Acked-by: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Link: https://lore.kernel.org/r/20200902133200.666781610@xxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/entry/common.c | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)
--- a/arch/x86/entry/common.c
+++ b/arch/x86/entry/common.c
@@ -55,8 +55,16 @@ static noinstr void check_user_regs(stru
* 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));
