From db5b2c5a90a111618f071d231a8b945cf522313e Mon Sep 17 00:00:00 2001 From: Andy Lutomirski Date: Fri, 3 Jul 2020 10:02:53 -0700 Subject: [PATCH] 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: ffae641f5747 ("x86/entry/64/compat: Fix Xen PV SYSENTER frame setup") Signed-off-by: Andy Lutomirski Signed-off-by: Thomas Gleixner Acked-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/9d33b3f3216dcab008070f1c28b6091ae7199969.1593795633.git.luto@kernel.org --- arch/x86/entry/entry_64_compat.S | 19 ++++++++++--------- 1 file changed, 10 insertions(+), 9 deletions(-) diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S index 381a6de7de9c..541fdaf64045 100644 --- a/arch/x86/entry/entry_64_compat.S +++ b/arch/x86/entry/entry_64_compat.S @@ -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 */