[PATCH 6.1 130/215] x86/decompressor: Store boot_params pointer in callee save register

Greg Kroah-Hartman
2024-03-04T21:48:19Z

From: Ard Biesheuvel <ardb@kernel.org>

commit 8b63cba746f86a754d66e302c43209cc9b9b6e39 upstream.

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: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20230807162720.545787-8-ardb@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/x86/boot/compressed/head_64.S | 42 ++++++++++++++-----------------------
1 file changed, 16 insertions(+), 26 deletions(-)

--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -408,10 +408,14 @@ 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
/*
@@ -422,12 +426,10 @@ 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

/*
@@ -440,13 +442,10 @@ 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
@@ -459,9 +458,9 @@ 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.
@@ -478,9 +477,9 @@ 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
@@ -490,14 +489,9 @@ 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
@@ -507,7 +501,6 @@ 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
@@ -515,7 +508,6 @@ trampoline_return:
std
rep movsq
cld
- popq %rsi

/*
* The GDT may get overwritten either during the copy we just did or
@@ -562,30 +554,28 @@ 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)