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* [PATCH AUTOSEL 6.6 1/9] x86/kexec: Allocate PGD for x86_64 transition page tables separately
@ 2025-01-26 15:08 Sasha Levin
  2025-01-26 15:08 ` [PATCH AUTOSEL 6.6 2/9] iommu/arm-smmu-qcom: add sdm670 adreno iommu compatible Sasha Levin
                   ` (7 more replies)
  0 siblings, 8 replies; 9+ messages in thread
From: Sasha Levin @ 2025-01-26 15:08 UTC (permalink / raw)
  To: linux-kernel, stable
  Cc: David Woodhouse, Ingo Molnar, Baoquan He, Vivek Goyal,
	Dave Young, Eric Biederman, Ard Biesheuvel, H. Peter Anvin,
	Sasha Levin, tglx, mingo, bp, dave.hansen, x86, hbathini,
	sourabhjain, tzimmermann, steve.wahl, david.kaplan, ltao

From: David Woodhouse <dwmw@amazon.co.uk>

[ Upstream commit 4b5bc2ec9a239bce261ffeafdd63571134102323 ]

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
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 arch/x86/include/asm/kexec.h       | 18 +++++++++---
 arch/x86/kernel/machine_kexec_64.c | 45 ++++++++++++++++--------------
 2 files changed, 38 insertions(+), 25 deletions(-)

diff --git a/arch/x86/include/asm/kexec.h b/arch/x86/include/asm/kexec.h
index c9f6a6c5de3cf..d54dd7084a3e1 100644
--- a/arch/x86/include/asm/kexec.h
+++ b/arch/x86/include/asm/kexec.h
@@ -16,6 +16,7 @@
 # define PAGES_NR		4
 #endif
 
+# define KEXEC_CONTROL_PAGE_SIZE	4096
 # define KEXEC_CONTROL_CODE_MAX_SIZE	2048
 
 #ifndef __ASSEMBLY__
@@ -44,7 +45,6 @@ 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
@@ -59,9 +59,6 @@ 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
@@ -146,6 +143,19 @@ 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;
diff --git a/arch/x86/kernel/machine_kexec_64.c b/arch/x86/kernel/machine_kexec_64.c
index 2fa12d1dc6760..8509d809a9f1b 100644
--- a/arch/x86/kernel/machine_kexec_64.c
+++ b/arch/x86/kernel/machine_kexec_64.c
@@ -149,7 +149,8 @@ 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;
@@ -160,7 +161,7 @@ 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);
@@ -219,7 +220,7 @@ 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,
@@ -228,12 +229,12 @@ 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;
@@ -247,8 +248,8 @@ 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;
 	}
@@ -263,8 +264,8 @@ 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;
@@ -274,15 +275,19 @@ 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)
@@ -299,14 +304,14 @@ 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;
 
@@ -360,13 +365,12 @@ 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)
@@ -574,8 +578,7 @@ 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);
 }
-- 
2.39.5


^ permalink raw reply	[flat|nested] 9+ messages in thread
end of thread, other threads:[~2025-01-26 15:09 UTC | newest]

Thread overview: 9+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2025-01-26 15:08 [PATCH AUTOSEL 6.6 1/9] x86/kexec: Allocate PGD for x86_64 transition page tables separately Sasha Levin
2025-01-26 15:08 ` [PATCH AUTOSEL 6.6 2/9] iommu/arm-smmu-qcom: add sdm670 adreno iommu compatible Sasha Levin
2025-01-26 15:08 ` [PATCH AUTOSEL 6.6 3/9] tool api fs: Correctly encode errno for read/write open failures Sasha Levin
2025-01-26 15:08 ` [PATCH AUTOSEL 6.6 4/9] iommu/arm-smmu-v3: Clean up more on probe failure Sasha Levin
2025-01-26 15:08 ` [PATCH AUTOSEL 6.6 5/9] platform/x86: int3472: Check for adev == NULL Sasha Levin
2025-01-26 15:08 ` [PATCH AUTOSEL 6.6 6/9] ASoC: soc-pcm: don't use soc_pcm_ret() on .prepare callback Sasha Levin
2025-01-26 15:08 ` [PATCH AUTOSEL 6.6 7/9] ASoC: amd: Add ACPI dependency to fix build error Sasha Levin
2025-01-26 15:08 ` [PATCH AUTOSEL 6.6 8/9] Input: allocate keycode for phone linking Sasha Levin
2025-01-26 15:08 ` [PATCH AUTOSEL 6.6 9/9] platform/x86: acer-wmi: Ignore AC events Sasha Levin

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