Merge tag 'for-linus-5.17' of git://git.kernel.org/pub/scm/virt/kvm/kvm

Pull kvm fix from Paolo Bonzini:
 "Fix for the SLS mitigation, which makes a 'SETcc/RET' pair grow
  to 'SETcc/RET/INT3'.

  This doesn't fit in 4 bytes any more, so the alignment has to
  change to 8 for this case"

* tag 'for-linus-5.17' of git://git.kernel.org/pub/scm/virt/kvm/kvm:
  kvm/emulate: Fix SETcc emulation function offsets with SLS

1 files changed, 17 insertions, 2 deletions

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 5719d8cfdbd9..e86d610dc6b7 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -429,8 +429,23 @@ static int fastop(struct x86_emulate_ctxt *ctxt, fastop_t fop);
 	FOP_END
 
 /* Special case for SETcc - 1 instruction per cc */
+
+/*
+ * Depending on .config the SETcc functions look like:
+ *
+ * SETcc %al   [3 bytes]
+ * RET         [1 byte]
+ * INT3        [1 byte; CONFIG_SLS]
+ *
+ * Which gives possible sizes 4 or 5.  When rounded up to the
+ * next power-of-two alignment they become 4 or 8.
+ */
+#define SETCC_LENGTH	(4 + IS_ENABLED(CONFIG_SLS))
+#define SETCC_ALIGN	(4 << IS_ENABLED(CONFIG_SLS))
+static_assert(SETCC_LENGTH <= SETCC_ALIGN);
+
 #define FOP_SETCC(op) \
-	".align 4 \n\t" \
+	".align " __stringify(SETCC_ALIGN) " \n\t" \
 	".type " #op ", @function \n\t" \
 	#op ": \n\t" \
 	#op " %al \n\t" \
@@ -1047,7 +1062,7 @@ 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