From: David Woodhouse <d...@amazon.co.uk>
A few places in the kexec control code page make the assumption that the
first instruction of relocate_kernel is at the very start of the page.
To allow for Clang CFI information to be added to relocate_kernel(), as
well as the general principle of removing unwarranted assumptions, fix
them to use the external __relocate_kernel_start symbol that the linker
adds. This means using a separate addq and subq for calculating offsets,
as the assembler can no longer calculate the delta directly for itself
and relocations aren't that versatile.
Turn the jump from relocate_kernel() to identity_mapped() into a real
indirect 'jmp *%rsi' too, while touching it. There was no real reason
for it to be a push+ret in the first place, and adding Clang CFI info
will also give objtool enough visibility to start complaining 'return
with modified stack frame' about it.
Signed-off-by: David Woodhouse <d...@amazon.co.uk>
---
arch/x86/kernel/relocate_kernel_64.S | 18 +++++++++++-------
1 file changed, 11 insertions(+), 7 deletions(-)
diff --git a/arch/x86/kernel/relocate_kernel_64.S
b/arch/x86/kernel/relocate_kernel_64.S
index 1996cea909ff..d74798d78263 100644
--- a/arch/x86/kernel/relocate_kernel_64.S
+++ b/arch/x86/kernel/relocate_kernel_64.S
@@ -95,11 +95,10 @@ SYM_CODE_START_NOALIGN(relocate_kernel)
lea PAGE_SIZE(%rsi), %rsp
/* jump to identity mapped page */
- addq $(identity_mapped - relocate_kernel), %rsi
- pushq %rsi
- ANNOTATE_UNRET_SAFE
- ret
- int3
+ addq $identity_mapped, %rsi
+ subq $__relocate_kernel_start, %rsi
+ ANNOTATE_RETPOLINE_SAFE
+ jmp *%rsi
SYM_CODE_END(relocate_kernel)
SYM_CODE_START_LOCAL_NOALIGN(identity_mapped)
@@ -219,16 +218,21 @@ SYM_CODE_START_LOCAL_NOALIGN(identity_mapped)
/* get the re-entry point of the peer system */
popq %rbp
- leaq relocate_kernel(%rip), %r8
movq kexec_pa_swap_page(%rip), %r10
movq pa_backup_pages_map(%rip), %rdi
movq kexec_pa_table_page(%rip), %rax
movq %rax, %cr3
+
+ /* Find start (and end) of this physical mapping of control page */
+ leaq (%rip), %r8
+ ANNOTATE_NOENDBR
+ andq $PAGE_MASK, %r8
lea PAGE_SIZE(%r8), %rsp
movq $1, %r11 /* Ensure preserve_context flag is set */
call swap_pages
movq kexec_va_control_page(%rip), %rax
- addq $(virtual_mapped - relocate_kernel), %rax
+ addq $virtual_mapped, %rax
+ subq $__relocate_kernel_start, %rax
pushq %rax
ANNOTATE_UNRET_SAFE
ret
--
2.47.0
