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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Lai Jiangshan <jiangshan.ljs@antgroup.com>,
        Borislav Petkov <bp@suse.de>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 5.15 348/667] x86/sev: Annotate stack change in the #VC handler
Date:   Tue,  7 Jun 2022 19:00:13 +0200
Message-Id: <20220607164945.196256488@linuxfoundation.org>
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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 e23319ad3f42..3acf0af49305 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