@@ -62,6 +62,7 @@ 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 /* Preserve boot_params pointer */
/* Set up the stack for verify_cpu() */
leaq (__end_init_task - PTREGS_SIZE)(%rip), %rsp
@@ -75,9 +76,7 @@ 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
@@ -95,10 +94,8 @@ 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 %r15, %rdi /* Pass boot_params pointer */
call sme_enable
- popq %rsi
#endif
/* Sanitize CPU configuration */
@@ -111,9 +108,7 @@ SYM_CODE_START_NOALIGN(startup_64)
* programmed into CR3.
*/
leaq _text(%rip), %rdi
- pushq %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 +122,6 @@ 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 +146,8 @@ SYM_INNER_LABEL(secondary_startup_64_no_verify, SYM_L_GLOBAL)
UNWIND_HINT_END_OF_STACK
ANNOTATE_NOENDBR
+ xorq %r15, %r15 /* Clear boot_params pointer */
+
/*
* 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 +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
@@ -365,9 +356,7 @@ 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 +392,7 @@ 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
+ movq %r15, %rdi /* Pass boot_params pointer */
.Ljump_to_C_code:
/*
Instead of pushing/popping %RSI to/from the stack every time a function is called from startup_64(), store it in callee preserved register R15 and grab it from there when its value is actually needed. Secondary boot does not and should not care about the value of %RSI at entry, and all the C handlers except the primary boot C entrypoint all ignore the function arguments entirely. Avoid inadvertent surprises by zeroing R15 on the secondary boot path explicitly. Signed-off-by: Ard Biesheuvel <ardb@kernel.org> --- arch/x86/kernel/head_64.S | 23 +++++--------------- 1 file changed, 5 insertions(+), 18 deletions(-)