4.20-stable review patch. If anyone has any objections, please let me know.
------------------
From: Jan Beulich JBeulich@suse.com
commit fc24d75a7f91837d7918e40719575951820b2b8f upstream.
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 jbeulich@suse.com Signed-off-by: Thomas Gleixner tglx@linutronix.de Reviewed-by: Juergen Gross jgross@suse.com Acked-by: Andy Lutomirski luto@kernel.org Cc: Peter Anvin hpa@zytor.com Cc: xen-devel@lists.xenproject.org> Cc: Boris Ostrovsky boris.ostrovsky@oracle.com Cc: stable@vger.kernel.org Link: https://lkml.kernel.org/r/5C3E1128020000780020DFAD@prv1-mh.provo.novell.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/x86/entry/entry_64_compat.S | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)
--- 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 */