Messages in this thread Patch in this message | | | From | Brian Gerst <> | Subject | [PATCH] x86/boot: Clean up handling of boot_params pointer | Date | Fri, 31 Mar 2023 14:28:39 -0400 |
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On entry from the bootloader, RSI contains the pointer to the boot_params data structure. Since the RSI register can be clobbered when calling C functions, it is saved and restored around every call. Instead, move it to the R12 register, which is preserved across calls.
Signed-off-by: Brian Gerst <brgerst@gmail.com> --- arch/x86/kernel/head_64.S | 29 ++++++++++------------------- 1 file changed, 10 insertions(+), 19 deletions(-)
diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S index a5df3e994f04..0d130ca2e0a3 100644 --- a/arch/x86/kernel/head_64.S +++ b/arch/x86/kernel/head_64.S @@ -49,8 +49,6 @@ 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. - * * We come here either directly from a 64bit bootloader, or from * arch/x86/boot/compressed/head_64.S. * @@ -61,6 +59,12 @@ SYM_CODE_START_NOALIGN(startup_64) * tables and then reload them. */ + /* + * RSI holds a physical pointer to real_mode_data. Move it to R12, + * which is preserved across C function calls. + */ + movq %rsi, %r12 + /* Set up the stack for verify_cpu() */ leaq (__end_init_task - PTREGS_SIZE)(%rip), %rsp @@ -73,9 +77,7 @@ SYM_CODE_START_NOALIGN(startup_64) shrq $32, %rdx wrmsr - pushq %rsi call startup_64_setup_env - popq %rsi #ifdef CONFIG_AMD_MEM_ENCRYPT /* @@ -84,10 +86,8 @@ SYM_CODE_START_NOALIGN(startup_64) * which needs to be done before any CPUID instructions are executed in * subsequent code. */ - movq %rsi, %rdi - pushq %rsi + movq %r12, %rdi call sme_enable - popq %rsi #endif /* Now switch to __KERNEL_CS so IRET works reliably */ @@ -109,9 +109,8 @@ SYM_CODE_START_NOALIGN(startup_64) * programmed into CR3. */ leaq _text(%rip), %rdi - pushq %rsi + movq %r12, %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 @@ -125,8 +124,6 @@ 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). * @@ -197,13 +194,9 @@ 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 @@ -294,9 +287,7 @@ 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 @@ -332,9 +323,9 @@ SYM_INNER_LABEL(secondary_startup_64_no_verify, SYM_L_GLOBAL) pushq $0 popfq - /* rsi is pointer to real mode structure with interesting info. + /* R12 is pointer to real mode structure with interesting info. pass it to C */ - movq %rsi, %rdi + movq %r12, %rdi .Ljump_to_C_code: /* -- 2.39.2
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