linux-kernel - [PATCH v3 10/17] x86/compressed: pull global variable ref up into startup32_load

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Date:   Tue, 22 Nov 2022 17:10:10 +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 10/17] x86/compressed: pull global variable ref up into startup32_load_idt()

In preparation for moving startup32_load_idt() out of head_64.S and
turning it into an ordinary function using the ordinary 32-bit calling
convention, pull the global variable reference to boot32_idt up into
startup32_load_idt() so that startup32_set_idt_entry() does not need to
discover its own runtime physical address, which will no longer be
correlated with startup_32 once this code is moved into .text.

While at it, give startup32_set_idt_entry() static linkage.

Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
---
 arch/x86/boot/compressed/head_64.S | 20 ++++++++------------
 1 file changed, 8 insertions(+), 12 deletions(-)

diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index f31277f455e63f5f..82d7fab99422129f 100644
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -736,16 +736,11 @@ SYM_DATA_END_LABEL(boot32_idt, SYM_L_GLOBAL, boot32_idt_end)
  *
  * %eax:	Handler address
  * %edx:	Vector number
- *
- * Physical offset is expected in %ebp
+ * %ecx:	IDT address
  */
-SYM_FUNC_START(startup32_set_idt_entry)
-	push    %ebx
-
-	/* IDT entry address to %ebx */
-	leal    rva(boot32_idt)(%ebp), %ebx
-	shl	$3, %edx
-	addl    %edx, %ebx
+SYM_FUNC_START_LOCAL(startup32_set_idt_entry)
+	/* IDT entry address to %ecx */
+	leal	(%ecx, %edx, 8), %ecx
 
 	/* Build IDT entry, lower 4 bytes */
 	movl    %eax, %edx
@@ -753,7 +748,7 @@ SYM_FUNC_START(startup32_set_idt_entry)
 	orl	$(__KERNEL32_CS << 16), %edx	# Target code segment selector
 
 	/* Store lower 4 bytes to IDT */
-	movl    %edx, (%ebx)
+	movl    %edx, (%ecx)
 
 	/* Build IDT entry, upper 4 bytes */
 	movl    %eax, %edx
@@ -761,15 +756,16 @@ SYM_FUNC_START(startup32_set_idt_entry)
 	orl     $0x00008e00, %edx	# Present, Type 32-bit Interrupt Gate
 
 	/* Store upper 4 bytes to IDT */
-	movl    %edx, 4(%ebx)
+	movl    %edx, 4(%ecx)
 
-	pop     %ebx
 	RET
 SYM_FUNC_END(startup32_set_idt_entry)
 #endif
 
 SYM_FUNC_START(startup32_load_idt)
 #ifdef CONFIG_AMD_MEM_ENCRYPT
+	leal    rva(boot32_idt)(%ebp), %ecx
+
 	/* #VC handler */
 	leal    rva(startup32_vc_handler)(%ebp), %eax
 	movl    $X86_TRAP_VC, %edx
-- 
2.35.1