Messages in this thread Patch in this message | | | Date | Wed, 02 Sep 2020 15:25:50 +0200 | From | Peter Zijlstra <> | Subject | [PATCH 01/13] x86/entry: Fix AC assertion |
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From: Peter Zijlstra <peterz@infradead.org>
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) <peterz@infradead.org> Acked-by: Andy Lutomirski <luto@kernel.org> --- 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));
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