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x86/boot/compressed: Move startup32_check_sev_cbit() into .text

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Move startup32_check_sev_cbit() into the .text section and turn it into
an ordinary function using the ordinary 32-bit calling convention,
instead of saving/restoring the registers that are known to be live at
the only call site. This improves maintainability, and makes it possible
to move this function out of head_64.S and into a separate compilation
unit that is specific to memory encryption.

Note that this requires the call site to be moved before the mixed mode
check, as %eax will be live otherwise.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/20221122161017.2426828-14-ardb@kernel.org
This commit is contained in:
Ard Biesheuvel 2022-11-22 17:10:13 +01:00 committed by Borislav Petkov
parent 9ea813be3d
commit b5d854cd4b
1 changed files with 19 additions and 16 deletions
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35
arch/x86/boot/compressed/head_64.S
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@ -251,6 +251,11 @@ SYM_FUNC_START(startup_32)
movl $__BOOT_TSS, %eax
ltr %ax
#ifdef CONFIG_AMD_MEM_ENCRYPT
/* Check if the C-bit position is correct when SEV is active */
call startup32_check_sev_cbit
#endif
/*
* Setup for the jump to 64bit mode
*
@ -268,8 +273,6 @@ SYM_FUNC_START(startup_32)
leal rva(startup_64_mixed_mode)(%ebp), %eax
1:
#endif
/* Check if the C-bit position is correct when SEV is active */
call startup32_check_sev_cbit
pushl $__KERNEL_CS
pushl %eax
@ -724,16 +727,17 @@ SYM_DATA_END_LABEL(boot_idt, SYM_L_GLOBAL, boot_idt_end)
* succeed. An incorrect C-bit position will map all memory unencrypted, so that
* the compare will use the encrypted random data and fail.
*/
__HEAD
SYM_FUNC_START(startup32_check_sev_cbit)
#ifdef CONFIG_AMD_MEM_ENCRYPT
pushl %eax
.text
SYM_FUNC_START(startup32_check_sev_cbit)
pushl %ebx
pushl %ecx
pushl %edx
pushl %ebp
call 0f
0: popl %ebp
/* Check for non-zero sev_status */
movl rva(sev_status)(%ebp), %eax
movl (sev_status - 0b)(%ebp), %eax
testl %eax, %eax
jz 4f
@ -748,17 +752,18 @@ SYM_FUNC_START(startup32_check_sev_cbit)
jnc 2b
/* Store to memory and keep it in the registers */
movl %eax, rva(sev_check_data)(%ebp)
movl %ebx, rva(sev_check_data+4)(%ebp)
leal (sev_check_data - 0b)(%ebp), %ebp
movl %eax, 0(%ebp)
movl %ebx, 4(%ebp)
/* Enable paging to see if encryption is active */
movl %cr0, %edx /* Backup %cr0 in %edx */
movl $(X86_CR0_PG | X86_CR0_PE), %ecx /* Enable Paging and Protected mode */
movl %ecx, %cr0
cmpl %eax, rva(sev_check_data)(%ebp)
cmpl %eax, 0(%ebp)
jne 3f
cmpl %ebx, rva(sev_check_data+4)(%ebp)
cmpl %ebx, 4(%ebp)
jne 3f
movl %edx, %cr0 /* Restore previous %cr0 */
@ -770,13 +775,11 @@ SYM_FUNC_START(startup32_check_sev_cbit)
jmp 3b
4:
popl %edx
popl %ecx
popl %ebp
popl %ebx
popl %eax
#endif
RET
SYM_FUNC_END(startup32_check_sev_cbit)
#endif
/*
* Stack and heap for uncompression