Instead of pushing/popping %RSI to/from the stack every time a function is called from startup_64(), store it in a callee preserved register and grab it from there when its value is actually needed. Signed-off-by: Ard Biesheuvel <ardb@xxxxxxxxxx> --- arch/x86/kernel/head_64.S | 32 ++++++++------------ 1 file changed, 12 insertions(+), 20 deletions(-) diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S index c5b9289837dcbad2..ea6995920b7aa920 100644 --- a/arch/x86/kernel/head_64.S +++ b/arch/x86/kernel/head_64.S @@ -51,7 +51,9 @@ SYM_CODE_START_NOALIGN(startup_64) * for us. These identity mapped page tables map all of the * kernel pages and possibly all of memory. * - * %rsi holds a physical pointer to real_mode_data. + * %RSI holds the physical address of the boot_params structure + * provided by the bootloader. Preserve it in %R15 so C function calls + * will not clobber it. * * We come here either directly from a 64bit bootloader, or from * arch/x86/boot/compressed/head_64.S. @@ -62,6 +64,7 @@ SYM_CODE_START_NOALIGN(startup_64) * compiled to run at we first fixup the physical addresses in our page * tables and then reload them. */ + mov %rsi, %r15 /* Set up the stack for verify_cpu() */ leaq (__end_init_task - PTREGS_SIZE)(%rip), %rsp @@ -75,9 +78,7 @@ SYM_CODE_START_NOALIGN(startup_64) shrq $32, %rdx wrmsr - pushq %rsi call startup_64_setup_env - popq %rsi /* Now switch to __KERNEL_CS so IRET works reliably */ pushq $__KERNEL_CS @@ -93,12 +94,10 @@ SYM_CODE_START_NOALIGN(startup_64) * Activate SEV/SME memory encryption if supported/enabled. This needs to * be done now, since this also includes setup of the SEV-SNP CPUID table, * which needs to be done before any CPUID instructions are executed in - * subsequent code. + * subsequent code. Pass the boot_params pointer as the first argument. */ - movq %rsi, %rdi - pushq %rsi + movq %r15, %rdi call sme_enable - popq %rsi #endif /* Sanitize CPU configuration */ @@ -111,9 +110,8 @@ SYM_CODE_START_NOALIGN(startup_64) * programmed into CR3. */ leaq _text(%rip), %rdi - pushq %rsi + movq %r15, %rsi call __startup_64 - popq %rsi /* Form the CR3 value being sure to include the CR3 modifier */ addq $(early_top_pgt - __START_KERNEL_map), %rax @@ -127,8 +125,6 @@ SYM_CODE_START(secondary_startup_64) * At this point the CPU runs in 64bit mode CS.L = 1 CS.D = 0, * and someone has loaded a mapped page table. * - * %rsi holds a physical pointer to real_mode_data. - * * We come here either from startup_64 (using physical addresses) * or from trampoline.S (using virtual addresses). * @@ -153,6 +149,9 @@ SYM_INNER_LABEL(secondary_startup_64_no_verify, SYM_L_GLOBAL) UNWIND_HINT_END_OF_STACK ANNOTATE_NOENDBR + /* Clear %R15 which holds the boot_params pointer on the boot CPU */ + xorq %r15, %r15 + /* * Retrieve the modifier (SME encryption mask if SME is active) to be * added to the initial pgdir entry that will be programmed into CR3. @@ -199,13 +198,9 @@ SYM_INNER_LABEL(secondary_startup_64_no_verify, SYM_L_GLOBAL) * hypervisor could lie about the C-bit position to perform a ROP * attack on the guest by writing to the unencrypted stack and wait for * the next RET instruction. - * %rsi carries pointer to realmode data and is callee-clobbered. Save - * and restore it. */ - pushq %rsi movq %rax, %rdi call sev_verify_cbit - popq %rsi /* * Switch to new page-table @@ -365,9 +360,7 @@ SYM_INNER_LABEL(secondary_startup_64_no_verify, SYM_L_GLOBAL) wrmsr /* Setup and Load IDT */ - pushq %rsi call early_setup_idt - popq %rsi /* Check if nx is implemented */ movl $0x80000001, %eax @@ -403,9 +396,8 @@ SYM_INNER_LABEL(secondary_startup_64_no_verify, SYM_L_GLOBAL) pushq $0 popfq - /* rsi is pointer to real mode structure with interesting info. - pass it to C */ - movq %rsi, %rdi + /* Pass the boot_params pointer as first argument */ + movq %r15, %rdi .Ljump_to_C_code: /* -- 2.39.2
