From: Jan Beulich Date: Tue, 15 Jan 2019 16:58:16 +0000 (-0700) Subject: x86/entry/64/compat: Fix stack switching for XEN PV X-Git-Url: http://git.cdn.openwrt.org/?a=commitdiff_plain;h=fc24d75a7f91837d7918e40719575951820b2b8f;p=openwrt%2Fstaging%2Fblogic.git x86/entry/64/compat: Fix stack switching for XEN PV While in the native case entry into the kernel happens on the trampoline stack, PV Xen kernels get entered with the current thread stack right away. Hence source and destination stacks are identical in that case, and special care is needed. Other than in sync_regs() the copying done on the INT80 path isn't NMI / #MC safe, as either of these events occurring in the middle of the stack copying would clobber data on the (source) stack. There is similar code in interrupt_entry() and nmi(), but there is no fixup required because those code paths are unreachable in XEN PV guests. [ tglx: Sanitized subject, changelog, Fixes tag and stable mail address. Sigh ] Fixes: 7f2590a110b8 ("x86/entry/64: Use a per-CPU trampoline stack for IDT entries") Signed-off-by: Jan Beulich Signed-off-by: Thomas Gleixner Reviewed-by: Juergen Gross Acked-by: Andy Lutomirski Cc: Peter Anvin Cc: xen-devel@lists.xenproject.org> Cc: Boris Ostrovsky Cc: stable@vger.kernel.org Link: https://lkml.kernel.org/r/5C3E1128020000780020DFAD@prv1-mh.provo.novell.com --- diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S index 8eaf8952c408..39913770a44d 100644 --- a/arch/x86/entry/entry_64_compat.S +++ b/arch/x86/entry/entry_64_compat.S @@ -361,7 +361,8 @@ ENTRY(entry_INT80_compat) /* Need to switch before accessing the thread stack. */ SWITCH_TO_KERNEL_CR3 scratch_reg=%rdi - movq %rsp, %rdi + /* In the Xen PV case we already run on the thread stack. */ + ALTERNATIVE "movq %rsp, %rdi", "jmp .Lint80_keep_stack", X86_FEATURE_XENPV movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp pushq 6*8(%rdi) /* regs->ss */ @@ -370,8 +371,9 @@ ENTRY(entry_INT80_compat) pushq 3*8(%rdi) /* regs->cs */ pushq 2*8(%rdi) /* regs->ip */ 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 */