linux-kernel - [PATCH v3 02/17] x86/compressed: efi-mixed: move 32-bit entrypoint code into .text section

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Message-Id: <20221122161017.2426828-3-ardb@kernel.org>
Date:   Tue, 22 Nov 2022 17:10:02 +0100
From:   Ard Biesheuvel <ardb@...nel.org>
To:     linux-efi@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, Ard Biesheuvel <ardb@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Michael Roth <michael.roth@....com>
Subject: [PATCH v3 02/17] x86/compressed: efi-mixed: move 32-bit entrypoint code into .text section

Move the code that stores the arguments passed to the EFI entrypoint
into the .text section, so that it can be moved into a separate
compilation unit in a subsequent patch.

Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
---
 arch/x86/boot/compressed/head_64.S | 48 ++++++++++++++------
 1 file changed, 34 insertions(+), 14 deletions(-)

diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index 190b803eb78712e0..74aaffd22b7425f4 100644
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -311,24 +311,41 @@ SYM_FUNC_START(efi32_stub_entry)
 	popl	%ecx
 	popl	%edx
 	popl	%esi
+	jmp	efi32_entry
+SYM_FUNC_END(efi32_stub_entry)
 
+	.text
+/*
+ * This is the common EFI stub entry point for mixed mode.
+ *
+ * Arguments:	%ecx	image handle
+ * 		%edx	EFI system table pointer
+ *		%esi	struct bootparams pointer (or NULL when not using
+ *			the EFI handover protocol)
+ *
+ * Since this is the point of no return for ordinary execution, no registers
+ * are considered live except for the function parameters. [Note that the EFI
+ * stub may still exit and return to the firmware using the Exit() EFI boot
+ * service.]
+ */
+SYM_FUNC_START_LOCAL(efi32_entry)
 	call	1f
-1:	pop	%ebp
-	subl	$ rva(1b), %ebp
-
-	movl	%esi, rva(efi32_boot_args+8)(%ebp)
-SYM_INNER_LABEL(efi32_pe_stub_entry, SYM_L_LOCAL)
-	movl	%ecx, rva(efi32_boot_args)(%ebp)
-	movl	%edx, rva(efi32_boot_args+4)(%ebp)
-	movb	$0, rva(efi_is64)(%ebp)
+1:	pop	%ebx
 
 	/* Save firmware GDTR and code/data selectors */
-	sgdtl	rva(efi32_boot_gdt)(%ebp)
-	movw	%cs, rva(efi32_boot_cs)(%ebp)
-	movw	%ds, rva(efi32_boot_ds)(%ebp)
+	sgdtl	(efi32_boot_gdt - 1b)(%ebx)
+	movw	%cs, (efi32_boot_cs - 1b)(%ebx)
+	movw	%ds, (efi32_boot_ds - 1b)(%ebx)
 
 	/* Store firmware IDT descriptor */
-	sidtl	rva(efi32_boot_idt)(%ebp)
+	sidtl	(efi32_boot_idt - 1b)(%ebx)
+
+	/* Store boot arguments */
+	leal	(efi32_boot_args - 1b)(%ebx), %ebx
+	movl	%ecx, 0(%ebx)
+	movl	%edx, 4(%ebx)
+	movl	%esi, 8(%ebx)
+	movb	$0x0, 12(%ebx)          // efi_is64
 
 	/* Disable paging */
 	movl	%cr0, %eax
@@ -336,7 +353,8 @@ SYM_INNER_LABEL(efi32_pe_stub_entry, SYM_L_LOCAL)
 	movl	%eax, %cr0
 
 	jmp	startup_32
-SYM_FUNC_END(efi32_stub_entry)
+SYM_FUNC_END(efi32_entry)
+	__HEAD
 #endif
 
 	.code64
@@ -839,7 +857,9 @@ SYM_FUNC_START(efi32_pe_entry)
 	 */
 	subl	%esi, %ebx
 	movl	%ebx, rva(image_offset)(%ebp)	// save image_offset
-	jmp	efi32_pe_stub_entry
+	xorl	%esi, %esi
+	jmp	efi32_entry			// pass %ecx, %edx, %esi
+						// no other registers remain live
 
 2:	popl	%edi				// restore callee-save registers
 	popl	%ebx
-- 
2.35.1