Commit 662a0221 authored Sep 02, 2020 by Peter Zijlstra Committed by Thomas Gleixner Sep 04, 2020

x86/entry: Fix AC assertion



The WARN added in commit 3c73b81a ("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: 3c73b81a ("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

parent 2356bb4b

arch/x86/include/asm/entry-common.h

+10 −2

Original line number	Diff line number	Diff line
		@@ -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));

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