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x86/mm: Fix SME encryption stack ptr handling

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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.

Fixes: 6ebcb06071 ("x86/mm: Add support to encrypt the kernel in-place")
Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Brijesh Singh <brijesh.singh@amd.com>
Link: http://lkml.kernel.org/r/20170827163924.25552-1-bp@alien8.de
This commit is contained in:
Borislav Petkov 2017-08-27 18:39:24 +02:00 committed by Thomas Gleixner
parent ea2800ddb2
commit 6e0b52d406
1 changed files with 3 additions and 3 deletions
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6
arch/x86/mm/mem_encrypt_boot.S
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@ -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)