Commit db5b2c5a authored by Andy Lutomirski's avatar Andy Lutomirski Committed by Thomas Gleixner
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x86/entry/compat: Clear RAX high bits on Xen PV SYSENTER 



Move the clearing of the high bits of RAX after Xen PV joins the SYSENTER
path so that Xen PV doesn't skip it.

Arguably this code should be deleted instead, but that would belong in the
merge window.

Fixes: ffae641f ("x86/entry/64/compat: Fix Xen PV SYSENTER frame setup")
Signed-off-by: default avatarAndy Lutomirski <luto@kernel.org>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Acked-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/9d33b3f3216dcab008070f1c28b6091ae7199969.1593795633.git.luto@kernel.org
parent cced0b24

arch/x86/entry/entry_64_compat.S

+10 −9
Original line number Diff line number Diff line
@@ -57,15 +57,6 @@ SYM_CODE_START(entry_SYSENTER_compat) 


	movq	PER_CPU_VAR(cpu_current_top_of_stack), %rsp



	/*

	 * User tracing code (ptrace or signal handlers) might assume that

	 * the saved RAX contains a 32-bit number when we're invoking a 32-bit

	 * syscall.  Just in case the high bits are nonzero, zero-extend

	 * the syscall number.  (This could almost certainly be deleted

	 * with no ill effects.)

	 */

	movl	%eax, %eax



	/* Construct struct pt_regs on stack */

	pushq	$__USER32_DS		/* pt_regs->ss */

	pushq	$0			/* pt_regs->sp = 0 (placeholder) */
@@ -80,6 +71,16 @@ SYM_CODE_START(entry_SYSENTER_compat) 
	pushq	$__USER32_CS		/* pt_regs->cs */

	pushq	$0			/* pt_regs->ip = 0 (placeholder) */

SYM_INNER_LABEL(entry_SYSENTER_compat_after_hwframe, SYM_L_GLOBAL)



	/*

	 * User tracing code (ptrace or signal handlers) might assume that

	 * the saved RAX contains a 32-bit number when we're invoking a 32-bit

	 * syscall.  Just in case the high bits are nonzero, zero-extend

	 * the syscall number.  (This could almost certainly be deleted

	 * with no ill effects.)

	 */

	movl	%eax, %eax



	pushq	%rax			/* pt_regs->orig_ax */

	pushq	%rdi			/* pt_regs->di */

	pushq	%rsi			/* pt_regs->si */

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