From: Paolo Bonzini <pbonzini@redhat.com>

Date: Fri, 15 Jul 2022 07:34:55 -0400

Subject: KVM: emulate: do not adjust size of fastop and setcc subroutines

Git-commit: 79629181607e801c0b41b8790ac4ee2eb5d7bc3e

Patch-mainline: v5.19-rc7

References: bsc#1201930

Instead of doing complicated calculations to find the size of the subroutines

(which are even more complicated because they need to be stringified into

an asm statement), just hardcode to 16.

It is less dense for a few combinations of IBT/SLS/retbleed, but it has

the advantage of being really simple.

Cc: stable@vger.kernel.org # 5.15.x: 84e7051c0bc1: x86/kvm: fix FASTOP_SIZE when return thunks are enabled

Cc: stable@vger.kernel.org

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Acked-by: Borislav Petkov <bp@suse.de>

---

 arch/x86/kvm/emulate.c |   15 +++++++--------

 1 file changed, 7 insertions(+), 8 deletions(-)

--- a/arch/x86/kvm/emulate.c

+++ b/arch/x86/kvm/emulate.c

@@ -188,9 +188,6 @@

 #define X8(x...) X4(x), X4(x)

 #define X16(x...) X8(x), X8(x)

-#define NR_FASTOP (ilog2(sizeof(ulong)) + 1)

-#define FASTOP_SIZE 8

-

 /*

  * fastop functions have a special calling convention:

  *

@@ -206,8 +203,14 @@

  *

  * fastop functions are declared as taking a never-defined fastop parameter,

  * so they can't be called from C directly.

+ *

+ * The 16 byte alignment, considering 5 bytes for the RET thunk, 3 for ENDBR

+ * and 1 for the straight line speculation INT3, leaves 7 bytes for the

+ * body of the function.  Currently none is larger than 4.

  */

+#define FASTOP_SIZE	16

+

 struct fastop;

 struct opcode {

@@ -443,11 +446,7 @@ static int fastop(struct x86_emulate_ctx

  * RET | JMP __x86_return_thunk	[1,5 bytes; CONFIG_RETPOLINE]

  * INT3				[1 byte; CONFIG_SLS]

  */

-#define RET_LENGTH	(1 + (4 * IS_ENABLED(CONFIG_RETPOLINE)) + \

-			 IS_ENABLED(CONFIG_SLS))

-#define SETCC_LENGTH	(3 + RET_LENGTH)

-#define SETCC_ALIGN	(4 << ((SETCC_LENGTH > 4) & 1) << ((SETCC_LENGTH > 8) & 1))

-static_assert(SETCC_LENGTH <= SETCC_ALIGN);

+#define SETCC_ALIGN	16

 /* Special case for SETcc - 1 instruction per cc */

 #define FOP_SETCC(op) \