[PATCH v3] x86,entry: Use PUSH_AND_CLEAR_REGS for compat

[Peter Zijlstra <peterz@infradead.org>]

Since the upper regs don't exist for ia32 code, preserving them
doesn't hurt and it simplifies the code.

If there was any attack surface on this, that attack surface already
exists for INT80 and needs to be otherwise dealt with.

Notably:

 - SYSENTER: didn't clear si, dx, cx.
 - SYSCALL, INT80: *do* clear si since the C functions don't take a
   second argument.

Add a clear_rsi argument to CLEAR_REGS for these 3 sites, and have
SYSENTER clear everything (no code relies on those registers not being
cleared and selftests pass).

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---

diff --git a/arch/x86/entry/calling.h b/arch/x86/entry/calling.h
index a4c061fb7c6e..526eba74b84c 100644
--- a/arch/x86/entry/calling.h
+++ b/arch/x86/entry/calling.h
@@ -63,13 +63,15 @@ For 32-bit we have the following conventions - kernel is built with
  * for assembly code:
  */
 
-.macro PUSH_REGS rdx=%rdx rax=%rax save_ret=0
+.macro PUSH_REGS rdx=%rdx rax=%rax save_ret=0 save_rdi=1
 	.if \save_ret
 	pushq	%rsi		/* pt_regs->si */
 	movq	8(%rsp), %rsi	/* temporarily store the return address in %rsi */
 	movq	%rdi, 8(%rsp)	/* pt_regs->di (overwriting original return address) */
 	.else
+	.if \save_rdi
 	pushq   %rdi		/* pt_regs->di */
+	.endif
 	pushq   %rsi		/* pt_regs->si */
 	.endif
 	pushq	\rdx		/* pt_regs->dx */
@@ -92,13 +94,16 @@ For 32-bit we have the following conventions - kernel is built with
 	.endif
 .endm
 
-.macro CLEAR_REGS
+.macro CLEAR_REGS clear_rsi=0
 	/*
 	 * Sanitize registers of values that a speculation attack might
 	 * otherwise want to exploit. The lower registers are likely clobbered
 	 * well before they could be put to use in a speculative execution
 	 * gadget.
 	 */
+	.if \clear_rsi
+	xorl	%esi,  %esi	/* nospec si  */
+	.endif
 	xorl	%edx,  %edx	/* nospec dx  */
 	xorl	%ecx,  %ecx	/* nospec cx  */
 	xorl	%r8d,  %r8d	/* nospec r8  */
@@ -111,12 +116,11 @@ For 32-bit we have the following conventions - kernel is built with
 	xorl	%r13d, %r13d	/* nospec r13 */
 	xorl	%r14d, %r14d	/* nospec r14 */
 	xorl	%r15d, %r15d	/* nospec r15 */
-
 .endm
 
-.macro PUSH_AND_CLEAR_REGS rdx=%rdx rax=%rax save_ret=0
-	PUSH_REGS rdx=\rdx, rax=\rax, save_ret=\save_ret
-	CLEAR_REGS
+.macro PUSH_AND_CLEAR_REGS rdx=%rdx rax=%rax save_ret=0 save_rdi=1 clear_rsi=0
+	PUSH_REGS rdx=\rdx, rax=\rax, save_ret=\save_ret save_rdi=\save_rdi
+	CLEAR_REGS clear_rsi=\clear_rsi
 .endm
 
 .macro POP_REGS pop_rdi=1 skip_r11rcx=0
diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S
index 4fdb007cddbd..4ca8d6bfbe6b 100644
--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@@ -83,32 +83,7 @@ SYM_INNER_LABEL(entry_SYSENTER_compat_after_hwframe, SYM_L_GLOBAL)
 	movl	%eax, %eax
 
 	pushq	%rax			/* pt_regs->orig_ax */
-	pushq	%rdi			/* pt_regs->di */
-	pushq	%rsi			/* pt_regs->si */
-	pushq	%rdx			/* pt_regs->dx */
-	pushq	%rcx			/* pt_regs->cx */
-	pushq	$-ENOSYS		/* pt_regs->ax */
-	pushq   $0			/* pt_regs->r8  = 0 */
-	xorl	%r8d, %r8d		/* nospec   r8 */
-	pushq   $0			/* pt_regs->r9  = 0 */
-	xorl	%r9d, %r9d		/* nospec   r9 */
-	pushq   $0			/* pt_regs->r10 = 0 */
-	xorl	%r10d, %r10d		/* nospec   r10 */
-	pushq   $0			/* pt_regs->r11 = 0 */
-	xorl	%r11d, %r11d		/* nospec   r11 */
-	pushq   %rbx                    /* pt_regs->rbx */
-	xorl	%ebx, %ebx		/* nospec   rbx */
-	pushq   %rbp                    /* pt_regs->rbp (will be overwritten) */
-	xorl	%ebp, %ebp		/* nospec   rbp */
-	pushq   $0			/* pt_regs->r12 = 0 */
-	xorl	%r12d, %r12d		/* nospec   r12 */
-	pushq   $0			/* pt_regs->r13 = 0 */
-	xorl	%r13d, %r13d		/* nospec   r13 */
-	pushq   $0			/* pt_regs->r14 = 0 */
-	xorl	%r14d, %r14d		/* nospec   r14 */
-	pushq   $0			/* pt_regs->r15 = 0 */
-	xorl	%r15d, %r15d		/* nospec   r15 */
-
+	PUSH_AND_CLEAR_REGS rax=$-ENOSYS clear_rsi=1
 	UNWIND_HINT_REGS
 
 	cld
@@ -225,35 +200,7 @@ SYM_INNER_LABEL(entry_SYSCALL_compat_safe_stack, SYM_L_GLOBAL)
 SYM_INNER_LABEL(entry_SYSCALL_compat_after_hwframe, SYM_L_GLOBAL)
 	movl	%eax, %eax		/* discard orig_ax high bits */
 	pushq	%rax			/* pt_regs->orig_ax */
-	pushq	%rdi			/* pt_regs->di */
-	pushq	%rsi			/* pt_regs->si */
-	xorl	%esi, %esi		/* nospec   si */
-	pushq	%rdx			/* pt_regs->dx */
-	xorl	%edx, %edx		/* nospec   dx */
-	pushq	%rbp			/* pt_regs->cx (stashed in bp) */
-	xorl	%ecx, %ecx		/* nospec   cx */
-	pushq	$-ENOSYS		/* pt_regs->ax */
-	pushq   $0			/* pt_regs->r8  = 0 */
-	xorl	%r8d, %r8d		/* nospec   r8 */
-	pushq   $0			/* pt_regs->r9  = 0 */
-	xorl	%r9d, %r9d		/* nospec   r9 */
-	pushq   $0			/* pt_regs->r10 = 0 */
-	xorl	%r10d, %r10d		/* nospec   r10 */
-	pushq   $0			/* pt_regs->r11 = 0 */
-	xorl	%r11d, %r11d		/* nospec   r11 */
-	pushq   %rbx                    /* pt_regs->rbx */
-	xorl	%ebx, %ebx		/* nospec   rbx */
-	pushq   %rbp                    /* pt_regs->rbp (will be overwritten) */
-	xorl	%ebp, %ebp		/* nospec   rbp */
-	pushq   $0			/* pt_regs->r12 = 0 */
-	xorl	%r12d, %r12d		/* nospec   r12 */
-	pushq   $0			/* pt_regs->r13 = 0 */
-	xorl	%r13d, %r13d		/* nospec   r13 */
-	pushq   $0			/* pt_regs->r14 = 0 */
-	xorl	%r14d, %r14d		/* nospec   r14 */
-	pushq   $0			/* pt_regs->r15 = 0 */
-	xorl	%r15d, %r15d		/* nospec   r15 */
-
+	PUSH_AND_CLEAR_REGS rax=$-ENOSYS clear_rsi=1
 	UNWIND_HINT_REGS
 
 	movq	%rsp, %rdi
@@ -381,35 +328,7 @@ SYM_CODE_START(entry_INT80_compat)
 	pushq	1*8(%rdi)		/* regs->orig_ax */
 	pushq	(%rdi)			/* pt_regs->di */
 .Lint80_keep_stack:
-
-	pushq	%rsi			/* pt_regs->si */
-	xorl	%esi, %esi		/* nospec   si */
-	pushq	%rdx			/* pt_regs->dx */
-	xorl	%edx, %edx		/* nospec   dx */
-	pushq	%rcx			/* pt_regs->cx */
-	xorl	%ecx, %ecx		/* nospec   cx */
-	pushq	$-ENOSYS		/* pt_regs->ax */
-	pushq   %r8			/* pt_regs->r8 */
-	xorl	%r8d, %r8d		/* nospec   r8 */
-	pushq   %r9			/* pt_regs->r9 */
-	xorl	%r9d, %r9d		/* nospec   r9 */
-	pushq   %r10			/* pt_regs->r10*/
-	xorl	%r10d, %r10d		/* nospec   r10 */
-	pushq   %r11			/* pt_regs->r11 */
-	xorl	%r11d, %r11d		/* nospec   r11 */
-	pushq   %rbx                    /* pt_regs->rbx */
-	xorl	%ebx, %ebx		/* nospec   rbx */
-	pushq   %rbp                    /* pt_regs->rbp */
-	xorl	%ebp, %ebp		/* nospec   rbp */
-	pushq   %r12                    /* pt_regs->r12 */
-	xorl	%r12d, %r12d		/* nospec   r12 */
-	pushq   %r13                    /* pt_regs->r13 */
-	xorl	%r13d, %r13d		/* nospec   r13 */
-	pushq   %r14                    /* pt_regs->r14 */
-	xorl	%r14d, %r14d		/* nospec   r14 */
-	pushq   %r15                    /* pt_regs->r15 */
-	xorl	%r15d, %r15d		/* nospec   r15 */
-
+	PUSH_AND_CLEAR_REGS rax=$-ENOSYS save_rdi=0 clear_rsi=1
 	UNWIND_HINT_REGS
 
 	cld