[tip: x86/boot] x86/boot/compressed: Move startup32_load_idt() into .text section

From: tip-bot2 for Ard Biesheuvel
Date: Thu Nov 24 2022 - 03:13:24 EST


The following commit has been merged into the x86/boot branch of tip:

Commit-ID: c6355995ba471d7ad574174e593192ce805c7e1a
Gitweb: https://git.kernel.org/tip/c6355995ba471d7ad574174e593192ce805c7e1a
Author: Ard Biesheuvel <ardb@xxxxxxxxxx>
AuthorDate: Tue, 22 Nov 2022 17:10:11 +01:00
Committer: Borislav Petkov <bp@xxxxxxx>
CommitterDate: Thu, 24 Nov 2022 08:57:41 +01:00

x86/boot/compressed: Move startup32_load_idt() into .text section

Convert startup32_load_idt() into an ordinary function and move it into
the .text section. This involves turning the rva() immediates into ones
derived from a local label, and preserving/restoring the %ebp and %ebx
as per the calling convention.

Also move the #ifdef to the only existing call site. This makes it clear
that the function call does nothing if support for memory encryption is
not compiled in.

Signed-off-by: Ard Biesheuvel <ardb@xxxxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Link: https://lore.kernel.org/r/20221122161017.2426828-12-ardb@xxxxxxxxxx
---
arch/x86/boot/compressed/head_64.S | 31 ++++++++++++++++++-----------
1 file changed, 20 insertions(+), 11 deletions(-)

diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index f9926b3..7aa147f 100644
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -118,7 +118,9 @@ SYM_FUNC_START(startup_32)
1:

/* Setup Exception handling for SEV-ES */
+#ifdef CONFIG_AMD_MEM_ENCRYPT
call startup32_load_idt
+#endif

/* Make sure cpu supports long mode. */
call verify_cpu
@@ -716,10 +718,8 @@ SYM_DATA_START(boot32_idt)
.quad 0
.endr
SYM_DATA_END_LABEL(boot32_idt, SYM_L_GLOBAL, boot32_idt_end)
-#endif

-#ifdef CONFIG_AMD_MEM_ENCRYPT
- __HEAD
+ .text
.code32
/*
* Write an IDT entry into boot32_idt
@@ -752,24 +752,32 @@ SYM_FUNC_START_LOCAL(startup32_set_idt_entry)

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
+ push %ebp
+ push %ebx
+
+ call 1f
+1: pop %ebp
+
+ leal (boot32_idt - 1b)(%ebp), %ebx

/* #VC handler */
- leal rva(startup32_vc_handler)(%ebp), %eax
+ leal (startup32_vc_handler - 1b)(%ebp), %eax
movl $X86_TRAP_VC, %edx
+ movl %ebx, %ecx
call startup32_set_idt_entry

/* Load IDT */
- leal rva(boot32_idt)(%ebp), %eax
- movl %eax, rva(boot32_idt_desc+2)(%ebp)
- lidt rva(boot32_idt_desc)(%ebp)
-#endif
+ leal (boot32_idt_desc - 1b)(%ebp), %ecx
+ movl %ebx, 2(%ecx)
+ lidt (%ecx)
+
+ pop %ebx
+ pop %ebp
RET
SYM_FUNC_END(startup32_load_idt)
+#endif

/*
* Check for the correct C-bit position when the startup_32 boot-path is used.
@@ -788,6 +796,7 @@ SYM_FUNC_END(startup32_load_idt)
* 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