Re: [PATCH v3 1/1] OvmfPkg/SecMain: Fix stack switching to permanent memory

["Song, Ge" <ge.song@hxt-semitech.com>]

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ge Song <ge.song@hxt-semitech.com>

Best Regards,
Songge

-----Original Message-----
From: songgebird@gmail.com [mailto:songgebird@gmail.com]
Sent: 2017年9月6日 11:12
To: edk2-devel@lists.01.org
Cc: Jordan Justen <jordan.l.justen@intel.com>; Laszlo Ersek <lersek@redhat.com>; Ard Biesheuvel <ard.biesheuvel@linaro.org>; Song, Ge <ge.song@hxt-semitech.com>
Subject: [PATCH v3 1/1] OvmfPkg/SecMain: Fix stack switching to permanent memory

From: Ge Song <ge.song@hxt-semitech.com>

In earlier PEI stage, temporary memory at PcdOvmfSecPeiTempRamBase is employed as stack and heap. We move them to the new room and do some relocation fixup when permanent memory becomes available.
TemporaryRamMigration() is responsible for switching the stack.

Before entering TemporaryRamMigration(), Ebp/Rbp is populated with the content of Esp/Rsp and used as frame pointer.

After the execution of SetJump/LongJump, stack migrates to new position while the context keeps unchanged.

But when TemporaryRamMigration() exits, Esp/Rsp is filled with the content of Ebp/Rbp to destroy this stack frame.

The result is, stack switches back to previous temporary memory.

When permanent memory becomes available, modules that have registered themselves for shadowing will be scheduled to execute. Some of them need to consume more memory(heap/stack). Contrast to temporary stack, permanent stack possesses larger space.

The potential risk is overflowing the stack if stack staying in temporary memory. When it happens, system may crash during S3 resume.

More detailed information:
> (gdb) disassemble /r
> Dump of assembler code for function TemporaryRamMigration:
>   0x00000000fffcd29c <+0>:55push   %rbp
>   0x00000000fffcd29d <+1>:48 89 e5mov    %rsp,%rbp
>   0x00000000fffcd2a0 <+4>:48 81 ec 70 01 00 00sub
> $0x170,%rsp
>    ...
>    ...
>    0x00000000fffcd425 <+393>:e8 80 10 00 00callq  0xfffce4aa
> <SaveAndSetDebugTimerInterrupt>
> => 0x00000000fffcd42a <+398>:b8 00 00 00 00mov    $0x0,%eax
>    0x00000000fffcd42f <+403>:c9leaveq
>    0x00000000fffcd430 <+404>:c3retq
> End of assembler dump.

See the description of leave(opcode: c9), from Intel 64 and IA-32 Architectures Software Developer's Manual, Volume 2A

"Releases the stack frame set up by an earlier ENTER instruction. The LEAVE instruction copies the frame pointer (in the EBP register) into the stack pointer register (ESP), which releases the stack space allocated to the stack frame. The old frame pointer (the frame pointer for the calling procedure that was saved by the ENTER instruction) is then popped from the stack into the EBP register, restoring the calling procedure’s stack frame."

To solve this, update Ebp/Rbp too when Esp/Rsp is updated

Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ge Song <ge.song@hxt-semitech.com>
Tested-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
---
 OvmfPkg/Sec/SecMain.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/OvmfPkg/Sec/SecMain.c b/OvmfPkg/Sec/SecMain.c index e1993ec347b5..f7fec3d8c03b 100644
--- a/OvmfPkg/Sec/SecMain.c
+++ b/OvmfPkg/Sec/SecMain.c
@@ -931,9 +931,11 @@ TemporaryRamMigration (
   if (SetJump (&JumpBuffer) == 0) {
 #if defined (MDE_CPU_IA32)
     JumpBuffer.Esp = JumpBuffer.Esp + DebugAgentContext.StackMigrateOffset;
+    JumpBuffer.Ebp = JumpBuffer.Ebp +
+ DebugAgentContext.StackMigrateOffset;
 #endif
 #if defined (MDE_CPU_X64)
     JumpBuffer.Rsp = JumpBuffer.Rsp + DebugAgentContext.StackMigrateOffset;
+    JumpBuffer.Rbp = JumpBuffer.Rbp +
+ DebugAgentContext.StackMigrateOffset;
 #endif
     LongJump (&JumpBuffer, (UINTN)-1);
   }
--
2.11.0




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