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x86/kexec: Allocate PGD for x86_64 transition page tables separately

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Now that the following fix:

  d0ceea662d45 ("x86/mm: Add _PAGE_NOPTISHADOW bit to avoid updating userspace page tables")

stops kernel_ident_mapping_init() from scribbling over the end of a
4KiB PGD by assuming the following 4KiB will be a userspace PGD,
there's no good reason for the kexec PGD to be part of a single
8KiB allocation with the control_code_page.

( It's not clear that that was the reason for x86_64 kexec doing it that
  way in the first place either; there were no comments to that effect and
  it seems to have been the case even before PTI came along. It looks like
  it was just a happy accident which prevented memory corruption on kexec. )

Either way, it definitely isn't needed now. Just allocate the PGD
separately on x86_64, like i386 already does.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Baoquan He <bhe@redhat.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Dave Young <dyoung@redhat.com>
Cc: Eric Biederman <ebiederm@xmission.com>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Link: https://lore.kernel.org/r/20241205153343.3275139-6-dwmw2@infradead.org
This commit is contained in:
David Woodhouse 2024-12-05 15:05:11 +00:00 committed by Ingo Molnar
parent 9e5683e2d0
commit 4b5bc2ec9a
2 changed files with 38 additions and 25 deletions
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18
arch/x86/include/asm/kexec.h
View File

@ -16,6 +16,7 @@
# define PAGES_NR 4
#endif
# define KEXEC_CONTROL_PAGE_SIZE 4096
# define KEXEC_CONTROL_CODE_MAX_SIZE 2048
#ifndef __ASSEMBLY__
@ -43,7 +44,6 @@ struct kimage;
/* Maximum address we can use for the control code buffer */
# define KEXEC_CONTROL_MEMORY_LIMIT TASK_SIZE
# define KEXEC_CONTROL_PAGE_SIZE 4096
/* The native architecture */
# define KEXEC_ARCH KEXEC_ARCH_386
@ -58,9 +58,6 @@ struct kimage;
/* Maximum address we can use for the control pages */
# define KEXEC_CONTROL_MEMORY_LIMIT (MAXMEM-1)
/* Allocate one page for the pdp and the second for the code */
# define KEXEC_CONTROL_PAGE_SIZE (4096UL + 4096UL)
/* The native architecture */
# define KEXEC_ARCH KEXEC_ARCH_X86_64
#endif
@ -145,6 +142,19 @@ struct kimage_arch {
};
#else
struct kimage_arch {
/*
* This is a kimage control page, as it must not overlap with either
* source or destination address ranges.
*/
pgd_t *pgd;
/*
* The virtual mapping of the control code page itself is used only
* during the transition, while the current kernel's pages are all
* in place. Thus the intermediate page table pages used to map it
* are not control pages, but instead just normal pages obtained
* with get_zeroed_page(). And have to be tracked (below) so that
* they can be freed.
*/
p4d_t *p4d;
pud_t *pud;
pmd_t *pmd;

45
arch/x86/kernel/machine_kexec_64.c
View File

@ -146,7 +146,8 @@ static void free_transition_pgtable(struct kimage *image)
image->arch.pte = NULL;
}
static int init_transition_pgtable(struct kimage *image, pgd_t *pgd)
static int init_transition_pgtable(struct kimage *image, pgd_t *pgd,
unsigned long control_page)
{
pgprot_t prot = PAGE_KERNEL_EXEC_NOENC;
unsigned long vaddr, paddr;
@ -157,7 +158,7 @@ static int init_transition_pgtable(struct kimage *image, pgd_t *pgd)
pte_t *pte;
vaddr = (unsigned long)relocate_kernel;
paddr = __pa(page_address(image->control_code_page)+PAGE_SIZE);
paddr = control_page;
pgd += pgd_index(vaddr);
if (!pgd_present(*pgd)) {
p4d = (p4d_t *)get_zeroed_page(GFP_KERNEL);
@ -216,7 +217,7 @@ static void *alloc_pgt_page(void *data)
return p;
}
static int init_pgtable(struct kimage *image, unsigned long start_pgtable)
static int init_pgtable(struct kimage *image, unsigned long control_page)
{
struct x86_mapping_info info = {
.alloc_pgt_page = alloc_pgt_page,
@ -225,12 +226,12 @@ static int init_pgtable(struct kimage *image, unsigned long start_pgtable)
.kernpg_flag = _KERNPG_TABLE_NOENC,
};
unsigned long mstart, mend;
pgd_t *level4p;
int result;
int i;
level4p = (pgd_t *)__va(start_pgtable);
clear_page(level4p);
image->arch.pgd = alloc_pgt_page(image);
if (!image->arch.pgd)
return -ENOMEM;
if (cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT)) {
info.page_flag |= _PAGE_ENC;
@ -244,8 +245,8 @@ static int init_pgtable(struct kimage *image, unsigned long start_pgtable)
mstart = pfn_mapped[i].start << PAGE_SHIFT;
mend = pfn_mapped[i].end << PAGE_SHIFT;
result = kernel_ident_mapping_init(&info,
level4p, mstart, mend);
result = kernel_ident_mapping_init(&info, image->arch.pgd,
mstart, mend);
if (result)
return result;
}
@ -260,8 +261,8 @@ static int init_pgtable(struct kimage *image, unsigned long start_pgtable)
mstart = image->segment[i].mem;
mend = mstart + image->segment[i].memsz;
result = kernel_ident_mapping_init(&info,
level4p, mstart, mend);
result = kernel_ident_mapping_init(&info, image->arch.pgd,
mstart, mend);
if (result)
return result;
@ -271,15 +272,19 @@ static int init_pgtable(struct kimage *image, unsigned long start_pgtable)
* Prepare EFI systab and ACPI tables for kexec kernel since they are
* not covered by pfn_mapped.
*/
result = map_efi_systab(&info, level4p);
result = map_efi_systab(&info, image->arch.pgd);
if (result)
return result;
result = map_acpi_tables(&info, level4p);
result = map_acpi_tables(&info, image->arch.pgd);
if (result)
return result;
return init_transition_pgtable(image, level4p);
/*
* This must be last because the intermediate page table pages it
* allocates will not be control pages and may overlap the image.
*/
return init_transition_pgtable(image, image->arch.pgd, control_page);
}
static void load_segments(void)
@ -296,14 +301,14 @@ static void load_segments(void)
int machine_kexec_prepare(struct kimage *image)
{
unsigned long start_pgtable;
unsigned long control_page;
int result;
/* Calculate the offsets */
start_pgtable = page_to_pfn(image->control_code_page) << PAGE_SHIFT;
control_page = page_to_pfn(image->control_code_page) << PAGE_SHIFT;
/* Setup the identity mapped 64bit page table */
result = init_pgtable(image, start_pgtable);
result = init_pgtable(image, control_page);
if (result)
return result;
@ -357,13 +362,12 @@ void machine_kexec(struct kimage *image)
#endif
}
control_page = page_address(image->control_code_page) + PAGE_SIZE;
control_page = page_address(image->control_code_page);
__memcpy(control_page, relocate_kernel, KEXEC_CONTROL_CODE_MAX_SIZE);
page_list[PA_CONTROL_PAGE] = virt_to_phys(control_page);
page_list[VA_CONTROL_PAGE] = (unsigned long)control_page;
page_list[PA_TABLE_PAGE] =
(unsigned long)__pa(page_address(image->control_code_page));
page_list[PA_TABLE_PAGE] = (unsigned long)__pa(image->arch.pgd);
if (image->type == KEXEC_TYPE_DEFAULT)
page_list[PA_SWAP_PAGE] = (page_to_pfn(image->swap_page)
@ -573,8 +577,7 @@ static void kexec_mark_crashkres(bool protect)
/* Don't touch the control code page used in crash_kexec().*/
control = PFN_PHYS(page_to_pfn(kexec_crash_image->control_code_page));
/* Control code page is located in the 2nd page. */
kexec_mark_range(crashk_res.start, control + PAGE_SIZE - 1, protect);
kexec_mark_range(crashk_res.start, control - 1, protect);
control += KEXEC_CONTROL_PAGE_SIZE;
kexec_mark_range(control, crashk_res.end, protect);
}