| From 94ed2b2c91fbdb10503f40e1117a6ec84f4c787d Mon Sep 17 00:00:00 2001 |
| From: Josh Poimboeuf <jpoimboe@redhat.com> |
| 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| no longer valid, which can result in the following ORC unwinder warning: |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 <vincent.weaver@maine.edu> |
| Reported-by: Dave Jones <dsj@fb.com> |
| Reported-by: Dr. David Alan Gilbert <dgilbert@redhat.com> |
| Reported-by: Joe Mario <jmario@redhat.com> |
| Reported-by: Jann Horn <jannh@google.com> |
| Reported-by: Linus Torvalds <torvalds@linux-foundation.org> |
| Reviewed-by: Miroslav Benes <mbenes@suse.cz> |
| Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com> |
| Signed-off-by: Ingo Molnar <mingo@kernel.org> |
| Cc: Andy Lutomirski <luto@kernel.org> |
| Cc: Peter Zijlstra <peterz@infradead.org> |
| Cc: Thomas Gleixner <tglx@linutronix.de> |
| Link: https://lore.kernel.org/r/60ea8f562987ed2d9ace2977502fe481c0d7c9a0.1587808742.git.jpoimboe@redhat.com |
| Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com> |
| |
| diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S |
| index c2604cb55c63..99b2f2670547 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 */ |
| -- |
| 2.7.4 |
| |