The following commit has been merged into the x86/boot branch of tip: Commit-ID: b25eb5f5e419b81f124d5ba2abaaacf1948fb97e Gitweb: https://git.kernel.org/tip/b25eb5f5e419b81f124d5ba2abaaacf1948fb97e Author: David Woodhouse <dwmw@xxxxxxxxxxxx> AuthorDate: Wed, 12 Mar 2025 14:34:13 Committer: Ingo Molnar <mingo@xxxxxxxxxx> CommitterDate: Fri, 14 Mar 2025 11:01:53 +01:00 x86/kexec: Add relocate_kernel() debugging support: Load a GDT There are some failure modes which lead to triple-faults in the relocate_kernel() function, which is fairly much undebuggable for normal mortals. Adding a GDT in the relocate_kernel() environment is step 1 towards being able to catch faults and do something more useful. Signed-off-by: David Woodhouse <dwmw@xxxxxxxxxxxx> Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx> Cc: Andy Lutomirski <luto@xxxxxxxxxx> Cc: Brian Gerst <brgerst@xxxxxxxxx> Cc: H. Peter Anvin <hpa@xxxxxxxxx> Cc: Kees Cook <keescook@xxxxxxxxxxxx> Cc: Ard Biesheuvel <ardb@xxxxxxxxxx> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Link: https://lore.kernel.org/r/20250312144257.2348250-2-dwmw2@xxxxxxxxxxxxx --- arch/x86/kernel/relocate_kernel_64.S | 23 +++++++++++++++++++++++ 1 file changed, 23 insertions(+) diff --git a/arch/x86/kernel/relocate_kernel_64.S b/arch/x86/kernel/relocate_kernel_64.S index b44d886..ac05897 100644 --- a/arch/x86/kernel/relocate_kernel_64.S +++ b/arch/x86/kernel/relocate_kernel_64.S @@ -40,6 +40,16 @@ SYM_DATA(kexec_pa_table_page, .quad 0) SYM_DATA(kexec_pa_swap_page, .quad 0) SYM_DATA_LOCAL(pa_backup_pages_map, .quad 0) + .balign 16 +SYM_DATA_START_LOCAL(kexec_debug_gdt) + .word kexec_debug_gdt_end - kexec_debug_gdt - 1 + .long 0 + .word 0 + .quad 0x00cf9a000000ffff /* __KERNEL32_CS */ + .quad 0x00af9a000000ffff /* __KERNEL_CS */ + .quad 0x00cf92000000ffff /* __KERNEL_DS */ +SYM_DATA_END_LABEL(kexec_debug_gdt, SYM_L_LOCAL, kexec_debug_gdt_end) + .section .text..relocate_kernel,"ax"; .code64 SYM_CODE_START_NOALIGN(relocate_kernel) @@ -116,6 +126,19 @@ SYM_CODE_START_LOCAL_NOALIGN(identity_mapped) /* store the start address on the stack */ pushq %rdx + /* Create a GDTR (16 bits limit, 64 bits addr) on stack */ + leaq kexec_debug_gdt(%rip), %rax + pushq %rax + pushw (%rax) + + /* Load the GDT, put the stack back */ + lgdt (%rsp) + addq $10, %rsp + + /* Test that we can load segments */ + movq %ds, %rax + movq %rax, %ds + /* * Clear X86_CR4_CET (if it was set) such that we can clear CR0_WP * below.
|