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x86/efi/mixed: Check CPU compatibility without relying on verify_cpu()

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In order for the EFI mixed mode startup code to be reusable in a context
where the legacy decompressor is not used, replace the call to
verify_cpu() [which performs an elaborate set of checks] with a simple
check against the 'long mode' bit in the appropriate CPUID leaf.

This is reasonable, given that EFI support is implied when booting in
this manner, and so there is no need to consider very old CPUs when
performing this check.

Acked-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
This commit is contained in:
Ard Biesheuvel
2025-01-07 15:57:16 +01:00
parent dac628e956
commit eaed895595
1 changed files with 9 additions and 13 deletions
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22
arch/x86/boot/compressed/efi_mixed.S
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@@ -279,24 +279,20 @@ SYM_FUNC_END(efi32_entry)
* efi_system_table_32_t *sys_table)
*/
SYM_FUNC_START(efi32_pe_entry)
pushl %ebp
movl %esp, %ebp
pushl %ebx // save callee-save registers
pushl %edi
call verify_cpu // check for long mode support
testl %eax, %eax
movl $0x80000003, %eax // EFI_UNSUPPORTED
jnz 2f
movl 8(%ebp), %ecx // image_handle
movl 12(%ebp), %edx // sys_table
/* Check whether the CPU supports long mode */
movl $0x80000001, %eax // assume extended info support
cpuid
btl $29, %edx // check long mode bit
jnc 1f
leal 8(%esp), %esp // preserve stack alignment
movl (%esp), %ecx // image_handle
movl 4(%esp), %edx // sys_table
jmp efi32_entry // pass %ecx, %edx
// no other registers remain live
2: popl %edi // restore callee-save registers
1: movl $0x80000003, %eax // EFI_UNSUPPORTED
popl %ebx
leave
RET
SYM_FUNC_END(efi32_pe_entry)