[PATCH 5.17 413/772] x86/sev: Annotate stack change in the #VC handler

Greg Kroah-Hartman
2022-06-07T21:13:01Z

From: Lai Jiangshan <jiangshan.ljs@antgroup.com>

[ Upstream commit c42b145181aafd59ed31ccd879493389e3ea5a08 ]

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: a13644f3a53d ("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
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/x86/entry/entry_64.S | 1 +
1 file changed, 1 insertion(+)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 466df3e50276..f7a0cc261b14 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -499,6 +499,7 @@ 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 */
--
2.35.1