lkml.org 
[lkml]   [2017]   [Aug]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH] x86/mm: Fix SME encryption stack ptr handling
Date
From: Borislav Petkov <bp@suse.de>

sme_encrypt_execute() stashes the stack pointer on entry into %rbp
because it allocates a one-page stack in the non-encrypted area for the
encryption routine to use. When the latter is done, it restores it from
%rbp again, before returning.

However, it uses the FRAME_* macros partially but restores %rsp from
%rbp explicitly with a MOV. And this is fine as long as the macros
*actually* do something.

Unless, you do a !CONFIG_FRAME_POINTER build where those macros
are empty. Then, we still restore %rsp from %rbp but %rbp contains
*something* and this leads to a stack corruption. The manifestation
being a triple-fault during early boot when testing SME. Good luck to me
debugging this with the clumsy endless-loop-in-asm method and narrowing
it down gradually. :-(

So, long story short, open-code the frame macros so that there's no
monkey business and we avoid subtly breaking SME depending on the
.config.

Signed-off-by: Borislav Petkov <bp@suse.de>
Acked-by: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Brijesh Singh <brijesh.singh@amd.com>
---
arch/x86/mm/mem_encrypt_boot.S | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/x86/mm/mem_encrypt_boot.S b/arch/x86/mm/mem_encrypt_boot.S
index b327e0472448..730e6d541df1 100644
--- a/arch/x86/mm/mem_encrypt_boot.S
+++ b/arch/x86/mm/mem_encrypt_boot.S
@@ -15,7 +15,6 @@
#include <asm/page.h>
#include <asm/processor-flags.h>
#include <asm/msr-index.h>
-#include <asm/frame.h>

.text
.code64
@@ -33,7 +32,8 @@ ENTRY(sme_encrypt_execute)
* R8 - physcial address of the pagetables to use for encryption
*/

- FRAME_BEGIN /* RBP now has original stack pointer */
+ push %rbp
+ movq %rsp, %rbp /* RBP now has original stack pointer */

/* Set up a one page stack in the non-encrypted memory area */
movq %rcx, %rax /* Workarea stack page */
@@ -64,7 +64,7 @@ ENTRY(sme_encrypt_execute)
pop %r12

movq %rbp, %rsp /* Restore original stack pointer */
- FRAME_END
+ pop %rbp

ret
ENDPROC(sme_encrypt_execute)
--
2.13.0
\
 
 \ /
  Last update: 2017-08-27 18:40    [W:0.058 / U:1.104 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site