Commit 8b63cba7 authored by Ard Biesheuvel's avatar Ard Biesheuvel Committed by Borislav Petkov (AMD)
Browse files

x86/decompressor: Store boot_params pointer in callee save register 



Instead of pushing and popping %RSI several times to preserve the struct
boot_params pointer across the execution of the startup code, move it
into a callee save register before the first call into C, and copy it
back when needed.

Signed-off-by: default avatarArd Biesheuvel <ardb@kernel.org>
Signed-off-by: default avatarBorislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20230807162720.545787-8-ardb@kernel.org
parent d7156b98

arch/x86/boot/compressed/head_64.S

+16 −26
Original line number Diff line number Diff line
@@ -405,10 +405,14 @@ SYM_CODE_START(startup_64) 
	lretq



.Lon_kernel_cs:

	/*

	 * RSI holds a pointer to a boot_params structure provided by the

	 * loader, and this needs to be preserved across C function calls. So

	 * move it into a callee saved register.

	 */

	movq	%rsi, %r15



	pushq	%rsi

	call	load_stage1_idt

	popq	%rsi



#ifdef CONFIG_AMD_MEM_ENCRYPT

	/*
@@ -419,12 +423,10 @@ SYM_CODE_START(startup_64) 
	 * CPUID instructions being issued, so go ahead and do that now via

	 * sev_enable(), which will also handle the rest of the SEV-related

	 * detection/setup to ensure that has been done in advance of any dependent

	 * code.

	 * code. Pass the boot_params pointer as the first argument.

	 */

	pushq	%rsi

	movq	%rsi, %rdi		/* real mode address */

	movq	%r15, %rdi

	call	sev_enable

	popq	%rsi

#endif



	/*
@@ -437,13 +439,10 @@ SYM_CODE_START(startup_64) 
	 *   - Non zero RDX means trampoline needs to enable 5-level

	 *     paging.

	 *

	 * RSI holds real mode data and needs to be preserved across

	 * this function call.

	 * Pass the boot_params pointer as the first argument.

	 */

	pushq	%rsi

	movq	%rsi, %rdi		/* real mode address */

	movq	%r15, %rdi

	call	paging_prepare

	popq	%rsi



	/* Save the trampoline address in RCX */

	movq	%rax, %rcx
@@ -456,9 +455,9 @@ SYM_CODE_START(startup_64) 
	 * because the architecture does not guarantee that GPRs will retain

	 * their full 64-bit values across a 32-bit mode switch.

	 */

	pushq	%r15

	pushq	%rbp

	pushq	%rbx

	pushq	%rsi



	/*

	 * Push the 64-bit address of trampoline_return() onto the new stack.
@@ -475,9 +474,9 @@ SYM_CODE_START(startup_64) 
	lretq

trampoline_return:

	/* Restore live 64-bit registers */

	popq	%rsi

	popq	%rbx

	popq	%rbp

	popq	%r15



	/* Restore the stack, the 32-bit trampoline uses its own stack */

	leaq	rva(boot_stack_end)(%rbx), %rsp
@@ -487,14 +486,9 @@ trampoline_return: 
	 *

	 * RDI is address of the page table to use instead of page table

	 * in trampoline memory (if required).

	 *

	 * RSI holds real mode data and needs to be preserved across

	 * this function call.

	 */

	pushq	%rsi

	leaq	rva(top_pgtable)(%rbx), %rdi

	call	cleanup_trampoline

	popq	%rsi



	/* Zero EFLAGS */

	pushq	$0
@@ -504,7 +498,6 @@ trampoline_return: 
 * Copy the compressed kernel to the end of our buffer

 * where decompression in place becomes safe.

 */

	pushq	%rsi

	leaq	(_bss-8)(%rip), %rsi

	leaq	rva(_bss-8)(%rbx), %rdi

	movl	$(_bss - startup_32), %ecx
@@ -512,7 +505,6 @@ trampoline_return: 
	std

	rep	movsq

	cld

	popq	%rsi



	/*

	 * The GDT may get overwritten either during the copy we just did or
@@ -544,30 +536,28 @@ SYM_FUNC_START_LOCAL_NOALIGN(.Lrelocated) 
	shrq	$3, %rcx

	rep	stosq



	pushq	%rsi

	call	load_stage2_idt



	/* Pass boot_params to initialize_identity_maps() */

	movq	(%rsp), %rdi

	movq	%r15, %rdi

	call	initialize_identity_maps

	popq	%rsi



/*

 * Do the extraction, and jump to the new kernel..

 */

	pushq	%rsi			/* Save the real mode argument */

	movq	%rsi, %rdi		/* real mode address */

	/* pass struct boot_params pointer */

	movq	%r15, %rdi

	leaq	boot_heap(%rip), %rsi	/* malloc area for uncompression */

	leaq	input_data(%rip), %rdx  /* input_data */

	movl	input_len(%rip), %ecx	/* input_len */

	movq	%rbp, %r8		/* output target address */

	movl	output_len(%rip), %r9d	/* decompressed length, end of relocs */

	call	extract_kernel		/* returns kernel entry point in %rax */

	popq	%rsi



/*

 * Jump to the decompressed kernel.

 */

	movq	%r15, %rsi

	jmp	*%rax

SYM_FUNC_END(.Lrelocated)