The following commit has been merged into the x86/boot branch of tip: Commit-ID: e536057543791fbfa0d979f4e782933ea312c38c Gitweb: https://git.kernel.org/tip/e536057543791fbfa0d979f4e782933ea312c38c Author: David Woodhouse <dwmw@xxxxxxxxxxxx> AuthorDate: Thu, 09 Jan 2025 14:04:20 Committer: Borislav Petkov (AMD) <bp@xxxxxxxxx> CommitterDate: Tue, 14 Jan 2025 13:05:14 +01:00 x86/kexec: Cope with relocate_kernel() not being at the start of the page 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. But those values can at least be used relative to a local label to avoid absolute relocations. 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. [ bp: Massage commit message. ] Signed-off-by: David Woodhouse <dwmw@xxxxxxxxxxxx> Signed-off-by: Borislav Petkov (AMD) <bp@xxxxxxxxx> Link: https://lore.kernel.org/r/20250109140757.2841269-9-dwmw2@xxxxxxxxxxxxx --- 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 14ed40b..af2cd06 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 +0: addq $identity_mapped - 0b, %rsi + subq $__relocate_kernel_start - 0b, %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 movl $1, %r11d /* Ensure preserve_context flag is set */ call swap_pages movq kexec_va_control_page(%rip), %rax - addq $(virtual_mapped - relocate_kernel), %rax +0: addq $virtual_mapped - 0b, %rax + subq $__relocate_kernel_start - 0b, %rax pushq %rax ANNOTATE_UNRET_SAFE ret
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