linux-kernel - Re: system locks up with CONFIG

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Message-ID: <YjI4u4VnkmzO+vQb@zn.tnic>
Date:   Wed, 16 Mar 2022 20:21:31 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: system locks up with CONFIG_SLS=Y; 5.17.0-rc

On Wed, Mar 16, 2022 at 12:02:59PM -0700, Dave Hansen wrote:
> This hit one of the new int3's in "ASM_RET" in "setc" in
> arch/x86/kvm/emulate.c:
> 
> 	FOP_SETCC(setc)
> 
> Did the extra 'int3' screw up some presumed jump offset or something?

Yap, looks like it. I wonder how no one managed to hit this yet...

Jamie, does this fix it, per chance?

---
diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index f667bd8df533..e88ce4171c4a 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -430,8 +430,11 @@ static int fastop(struct x86_emulate_ctxt *ctxt, fastop_t fop);
 	FOP_END
 
 /* Special case for SETcc - 1 instruction per cc */
+
+#define SETCC_ALIGN 8
+
 #define FOP_SETCC(op) \
-	".align 4 \n\t" \
+	".align " __stringify(SETCC_ALIGN) " \n\t" \
 	".type " #op ", @function \n\t" \
 	#op ": \n\t" \
 	ASM_ENDBR \
@@ -1049,7 +1052,7 @@ static int em_bsr_c(struct x86_emulate_ctxt *ctxt)
 static __always_inline u8 test_cc(unsigned int condition, unsigned long flags)
 {
 	u8 rc;
-	void (*fop)(void) = (void *)em_setcc + 4 * (condition & 0xf);
+	void (*fop)(void) = (void *)em_setcc + SETCC_ALIGN * (condition & 0xf);
 
 	flags = (flags & EFLAGS_MASK) | X86_EFLAGS_IF;
 	asm("push %[flags]; popf; " CALL_NOSPEC


-- 
Regards/Gruss,
    Boris.

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