[PATCH v2 11/16] x86/compressed: move startup32_load_idt() into .text section

Ard Biesheuvel
2022-09-21T14:55:59Z

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@kernel.org>
---
arch/x86/boot/compressed/head_64.S | 29 ++++++++++++++------
1 file changed, 20 insertions(+), 9 deletions(-)

diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index a1f893dd5bbf..b4b2b76ed1af 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
@@ -719,7 +721,7 @@ 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 +754,32 @@ 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 +798,7 @@ 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
--
2.35.1