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Mon, 10 Feb 2025 09:50:05 -0800 (PST) Date: Mon, 10 Feb 2025 18:49:44 +0100 In-Reply-To: <20250210174941.3251435-9-ardb+git@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20250210174941.3251435-9-ardb+git@google.com> X-Developer-Key: i=ardb@kernel.org; a=openpgp; fpr=F43D03328115A198C90016883D200E9CA6329909 X-Developer-Signature: v=1; a=openpgp-sha256; l=1856; i=ardb@kernel.org; h=from:subject; bh=/dO898kQXEjoQLrU/9r0JGYqSR+mG5aN2BZaklDsnBo=; b=owGbwMvMwCFmkMcZplerG8N4Wi2JIX2VjbnWyoAsrQP6J67N2Rw7Y9WXn3/+2ortybonx7Hsz uI6q73rOkpZGMQ4GGTFFFkEZv99t/P0RKla51myMHNYmUCGMHBxCsBEmK0ZGQ5LvRM+vD75fuSr bemFLnbSfk2L3kiyVD4zZGt6l2+zooPhf+1rF0lRRQ+9qsync07mV++Z9+8ab0LYujC5kiXM2uk HWAA= X-Mailer: git-send-email 2.48.1.502.g6dc24dfdaf-goog Message-ID: <20250210174941.3251435-11-ardb+git@google.com> Subject: [PATCH v2 2/7] x86/efi/mixed: Check CPU compatibility without relying on verify_cpu() From: Ard Biesheuvel To: linux-efi@vger.kernel.org Cc: linux-kernel@vger.kernel.org, x86@kernel.org, hdegoede@redhat.com, Ard Biesheuvel Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Ard Biesheuvel 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. Signed-off-by: Ard Biesheuvel --- arch/x86/boot/compressed/efi_mixed.S | 22 ++++++++------------ 1 file changed, 9 insertions(+), 13 deletions(-) diff --git a/arch/x86/boot/compressed/efi_mixed.S b/arch/x86/boot/compresse= d/efi_mixed.S index d681e30c6732..b7886e2591fc 100644 --- a/arch/x86/boot/compressed/efi_mixed.S +++ b/arch/x86/boot/compressed/efi_mixed.S @@ -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 =20 - 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) =20 --=20 2.48.1.362.g079036d154-goog