From 16aace664b2715dc4f7c88747eed27e035da8f5f Mon Sep 17 00:00:00 2001 From: Josh Poimboeuf Date: Sat, 25 Apr 2020 05:03:02 -0500 Subject: [PATCH] x86/entry/64: Fix unwind hints in kernel exit path commit 1fb143634a38095b641a3a21220774799772dc4c upstream. In swapgs_restore_regs_and_return_to_usermode, after the stack is switched to the trampoline stack, the existing UNWIND_HINT_REGS hint is no longer valid, which can result in the following ORC unwinder warning: WARNING: can't dereference registers at 000000003aeb0cdd for ip swapgs_restore_regs_and_return_to_usermode+0x93/0xa0 For full correctness, we could try to add complicated unwind hints so the unwinder could continue to find the registers, but when when it's this close to kernel exit, unwind hints aren't really needed anymore and it's fine to just use an empty hint which tells the unwinder to stop. For consistency, also move the UNWIND_HINT_EMPTY in entry_SYSCALL_64_after_hwframe to a similar location. Fixes: 3e3b9293d392 ("x86/entry/64: Return to userspace from the trampoline stack") Reported-by: Vince Weaver Reported-by: Dave Jones Reported-by: Dr. David Alan Gilbert Reported-by: Joe Mario Reported-by: Jann Horn Reported-by: Linus Torvalds Reviewed-by: Miroslav Benes Signed-off-by: Josh Poimboeuf Signed-off-by: Ingo Molnar Cc: Andy Lutomirski Cc: Peter Zijlstra Cc: Thomas Gleixner Link: https://lore.kernel.org/r/60ea8f562987ed2d9ace2977502fe481c0d7c9a0.1587808742.git.jpoimboe@redhat.com Signed-off-by: Greg Kroah-Hartman --- arch/x86/entry/entry_64.S | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S index b7c3ea4cb19d..cf6236ced532 100644 --- a/arch/x86/entry/entry_64.S +++ b/arch/x86/entry/entry_64.S @@ -249,7 +249,6 @@ GLOBAL(entry_SYSCALL_64_after_hwframe) */ syscall_return_via_sysret: /* rcx and r11 are already restored (see code above) */ - UNWIND_HINT_EMPTY POP_REGS pop_rdi=0 skip_r11rcx=1 /* @@ -258,6 +257,7 @@ syscall_return_via_sysret: */ movq %rsp, %rdi movq PER_CPU_VAR(cpu_tss_rw + TSS_sp0), %rsp + UNWIND_HINT_EMPTY pushq RSP-RDI(%rdi) /* RSP */ pushq (%rdi) /* RDI */ @@ -637,6 +637,7 @@ GLOBAL(swapgs_restore_regs_and_return_to_usermode) */ movq %rsp, %rdi movq PER_CPU_VAR(cpu_tss_rw + TSS_sp0), %rsp + UNWIND_HINT_EMPTY /* Copy the IRET frame to the trampoline stack. */ pushq 6*8(%rdi) /* SS */