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x86/entry: Fix AC assertion

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The WARN added in commit 3c73b81a91 ("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: 3c73b81a91 ("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
This commit is contained in:
Peter Zijlstra 2020-09-02 15:25:50 +02:00 committed by Thomas Gleixner
parent 2356bb4b82
commit 662a022189
1 changed files with 10 additions and 2 deletions
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12
arch/x86/include/asm/entry-common.h
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@ -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));