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x86/sev: Annotate stack change in the #VC handler

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In idtentry_vc(), vc_switch_off_ist() determines a safe stack to
switch to, off of the IST stack. Annotate the new stack switch with
ENCODE_FRAME_POINTER in case UNWINDER_FRAME_POINTER is used.

A stack walk before looks like this:

  CPU: 0 PID: 0 Comm: swapper Not tainted 5.18.0-rc7+ #2
  Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015
  Call Trace:
   <TASK>
   dump_stack_lvl
   dump_stack
   kernel_exc_vmm_communication
   asm_exc_vmm_communication
   ? native_read_msr
   ? __x2apic_disable.part.0
   ? x2apic_setup
   ? cpu_init
   ? trap_init
   ? start_kernel
   ? x86_64_start_reservations
   ? x86_64_start_kernel
   ? secondary_startup_64_no_verify
   </TASK>

and with the fix, the stack dump is exact:

  CPU: 0 PID: 0 Comm: swapper Not tainted 5.18.0-rc7+ #3
  Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015
  Call Trace:
   <TASK>
   dump_stack_lvl
   dump_stack
   kernel_exc_vmm_communication
   asm_exc_vmm_communication
  RIP: 0010:native_read_msr
  Code: ...
  < snipped regs >
   ? __x2apic_disable.part.0
   x2apic_setup
   cpu_init
   trap_init
   start_kernel
   x86_64_start_reservations
   x86_64_start_kernel
   secondary_startup_64_no_verify
   </TASK>

  [ bp: Test in a SEV-ES guest and rewrite the commit message to
    explain what exactly this does. ]

Fixes: a13644f3a5 ("x86/entry/64: Add entry code for #VC handler")
Signed-off-by: Lai Jiangshan <jiangshan.ljs@antgroup.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20220316041612.71357-1-jiangshanlai@gmail.com
This commit is contained in:
Lai Jiangshan 2022-03-16 12:16:12 +08:00 committed by Borislav Petkov
parent 0621210ab7
commit c42b145181
1 changed files with 1 additions and 0 deletions
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arch/x86/entry/entry_64.S
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@ -505,6 +505,7 @@ SYM_CODE_START(\asmsym)
call vc_switch_off_ist
movq %rax, %rsp /* Switch to new stack */
ENCODE_FRAME_POINTER
UNWIND_HINT_REGS
/* Update pt_regs */