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x86/kexec: Debugging support: Load an IDT and basic exception entry points

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[ mingo: Minor readability edits ]

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20250314173226.3062535-2-dwmw2@infradead.org
This commit is contained in:
David Woodhouse 2025-03-14 17:27:33 +00:00 committed by Ingo Molnar
parent 2df0c02dab
commit 8df505af7f
3 changed files with 103 additions and 0 deletions
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5
arch/x86/include/asm/kexec.h
View File

@ -8,6 +8,9 @@
# define PA_PGD 2
# define PA_SWAP_PAGE 3
# define PAGES_NR 4
#else
/* Size of each exception handler referenced by the IDT */
# define KEXEC_DEBUG_EXC_HANDLER_SIZE 6 /* PUSHI, PUSHI, 2-byte JMP */
#endif
# define KEXEC_CONTROL_PAGE_SIZE 4096
@ -59,6 +62,8 @@ struct kimage;
extern unsigned long kexec_va_control_page;
extern unsigned long kexec_pa_table_page;
extern unsigned long kexec_pa_swap_page;
extern gate_desc kexec_debug_idt[];
extern unsigned char kexec_debug_exc_vectors[];
#endif
/*

21
arch/x86/kernel/machine_kexec_64.c
View File

@ -304,6 +304,24 @@ static void load_segments(void)
);
}
static void prepare_debug_idt(unsigned long control_page, unsigned long vec_ofs)
{
gate_desc idtentry = { 0 };
int i;
idtentry.bits.p = 1;
idtentry.bits.type = GATE_TRAP;
idtentry.segment = __KERNEL_CS;
idtentry.offset_low = (control_page & 0xFFFF) + vec_ofs;
idtentry.offset_middle = (control_page >> 16) & 0xFFFF;
idtentry.offset_high = control_page >> 32;
for (i = 0; i < 16; i++) {
kexec_debug_idt[i] = idtentry;
idtentry.offset_low += KEXEC_DEBUG_EXC_HANDLER_SIZE;
}
}
int machine_kexec_prepare(struct kimage *image)
{
void *control_page = page_address(image->control_code_page);
@ -321,6 +339,9 @@ int machine_kexec_prepare(struct kimage *image)
if (image->type == KEXEC_TYPE_DEFAULT)
kexec_pa_swap_page = page_to_pfn(image->swap_page) << PAGE_SHIFT;
prepare_debug_idt((unsigned long)__pa(control_page),
(unsigned long)kexec_debug_exc_vectors - reloc_start);
__memcpy(control_page, __relocate_kernel_start, reloc_end - reloc_start);
set_memory_rox((unsigned long)control_page, 1);

77
arch/x86/kernel/relocate_kernel_64.S
View File

@ -50,6 +50,11 @@ SYM_DATA_START_LOCAL(kexec_debug_gdt)
.quad 0x00cf92000000ffff /* __KERNEL_DS */
SYM_DATA_END_LABEL(kexec_debug_gdt, SYM_L_LOCAL, kexec_debug_gdt_end)
.balign 8
SYM_DATA_START(kexec_debug_idt)
.skip 0x100, 0x00
SYM_DATA_END(kexec_debug_idt)
.section .text..relocate_kernel,"ax";
.code64
SYM_CODE_START_NOALIGN(relocate_kernel)
@ -139,6 +144,15 @@ SYM_CODE_START_LOCAL_NOALIGN(identity_mapped)
movq %ds, %rax
movq %rax, %ds
/* Now an IDTR on the stack to load the IDT the kernel created */
leaq kexec_debug_idt(%rip), %rsi
pushq %rsi
pushw $0xff
lidt (%rsp)
addq $10, %rsp
//int3
/*
* Clear X86_CR4_CET (if it was set) such that we can clear CR0_WP
* below.
@ -364,3 +378,66 @@ SYM_CODE_START_LOCAL_NOALIGN(swap_pages)
ret
int3
SYM_CODE_END(swap_pages)
SYM_CODE_START_NOALIGN(kexec_debug_exc_vectors)
/* Each of these is 6 bytes. */
.macro vec_err exc
UNWIND_HINT_ENTRY
. = kexec_debug_exc_vectors + (\exc * KEXEC_DEBUG_EXC_HANDLER_SIZE)
nop
nop
pushq $\exc
jmp exc_handler
.endm
.macro vec_noerr exc
UNWIND_HINT_ENTRY
. = kexec_debug_exc_vectors + (\exc * KEXEC_DEBUG_EXC_HANDLER_SIZE)
pushq $0
pushq $\exc
jmp exc_handler
.endm
ANNOTATE_NOENDBR
vec_noerr 0 // #DE
vec_noerr 1 // #DB
vec_noerr 2 // #NMI
vec_noerr 3 // #BP
vec_noerr 4 // #OF
vec_noerr 5 // #BR
vec_noerr 6 // #UD
vec_noerr 7 // #NM
vec_err 8 // #DF
vec_noerr 9
vec_err 10 // #TS
vec_err 11 // #NP
vec_err 12 // #SS
vec_err 13 // #GP
vec_err 14 // #PF
vec_noerr 15
SYM_CODE_END(kexec_debug_exc_vectors)
SYM_CODE_START_LOCAL_NOALIGN(exc_handler)
/* No need for RET mitigations during kexec */
VALIDATE_UNRET_END
pushq %rax
pushq %rdx
movw $0x3f8, %dx
movb $'A', %al
outb %al, %dx
popq %rdx
popq %rax
/* Only return from INT3 */
cmpq $3, (%rsp)
jne .Ldie
addq $16, %rsp
iretq
.Ldie:
hlt
jmp .Ldie
SYM_CODE_END(exc_handler)