[PATCH 5.15 37/78] x86/sev: Avoid using __x86_return_thunk

Greg Kroah-Hartman
2022-07-12T19:02:19Z

From: Kim Phillips <kim.phillips@amd.com>

commit 0ee9073000e8791f8b134a8ded31bcc767f7f232 upstream.

Specifically, it's because __enc_copy() encrypts the kernel after
being relocated outside the kernel in sme_encrypt_execute(), and the
RET macro's jmp offset isn't amended prior to execution.

Signed-off-by: Kim Phillips <kim.phillips@amd.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/x86/mm/mem_encrypt_boot.S | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)

--- a/arch/x86/mm/mem_encrypt_boot.S
+++ b/arch/x86/mm/mem_encrypt_boot.S
@@ -65,7 +65,9 @@ SYM_FUNC_START(sme_encrypt_execute)
movq %rbp, %rsp /* Restore original stack pointer */
pop %rbp

- RET
+ /* Offset to __x86_return_thunk would be wrong here */
+ ret
+ int3
SYM_FUNC_END(sme_encrypt_execute)

SYM_FUNC_START(__enc_copy)
@@ -151,6 +153,8 @@ SYM_FUNC_START(__enc_copy)
pop %r12
pop %r15

- RET
+ /* Offset to __x86_return_thunk would be wrong here */
+ ret
+ int3
.L__enc_copy_end:
SYM_FUNC_END(__enc_copy)