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Subject[Resend][PATCH] x86/power/64: Always create temporary identity mapping correctly
Date
From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

The low-level resume-from-hibernation code on x86-64 uses
kernel_ident_mapping_init() to create the temoprary identity mapping,
but that function assumes that the offset between kernel virtual
addresses and physical addresses is aligned on the PGD level.

However, with a randomized identity mapping base, it may be aligned
on the PUD level and if that happens, the temporary identity mapping
created by set_up_temporary_mappings() will not reflect the actual
kernel identity mapping and the image restoration will fail as a
result (leading to a kernel panic most of the time).

To fix this problem, rework kernel_ident_mapping_init() to support
unaligned offsets between KVA and PA up to the PMD level and make
set_up_temporary_mappings() use it as approprtiate.

Reported-by: Thomas Garnier <thgarnie@google.com>
Suggested-by: Yinghai Lu <yinghai@kernel.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Yinghai Lu <yinghai@kernel.org>
---

This is sort of urgent, because hibernation doesn't work with KASLR on x86-64
in 4.8-rc1 AFAICS and this should make them work together again.

Unless anyone sees any problems with it, I'll queue it up for 4.8-rc2.

Thomas, would it be possible to test it with KASLR enabled, please?

Thanks,
Rafael

---
arch/x86/include/asm/init.h | 4 ++--
arch/x86/mm/ident_map.c | 19 +++++++++++--------
arch/x86/power/hibernate_64.c | 2 +-
3 files changed, 14 insertions(+), 11 deletions(-)

Index: linux-pm/arch/x86/include/asm/init.h
===================================================================
--- linux-pm.orig/arch/x86/include/asm/init.h
+++ linux-pm/arch/x86/include/asm/init.h
@@ -5,10 +5,10 @@ struct x86_mapping_info {
void *(*alloc_pgt_page)(void *); /* allocate buf for page table */
void *context; /* context for alloc_pgt_page */
unsigned long pmd_flag; /* page flag for PMD entry */
- bool kernel_mapping; /* kernel mapping or ident mapping */
+ unsigned long offset; /* ident mapping offset */
};

int kernel_ident_mapping_init(struct x86_mapping_info *info, pgd_t *pgd_page,
- unsigned long addr, unsigned long end);
+ unsigned long pstart, unsigned long pend);

#endif /* _ASM_X86_INIT_H */
Index: linux-pm/arch/x86/mm/ident_map.c
===================================================================
--- linux-pm.orig/arch/x86/mm/ident_map.c
+++ linux-pm/arch/x86/mm/ident_map.c
@@ -3,15 +3,17 @@
* included by both the compressed kernel and the regular kernel.
*/

-static void ident_pmd_init(unsigned long pmd_flag, pmd_t *pmd_page,
+static void ident_pmd_init(struct x86_mapping_info *info, pmd_t *pmd_page,
unsigned long addr, unsigned long end)
{
addr &= PMD_MASK;
for (; addr < end; addr += PMD_SIZE) {
pmd_t *pmd = pmd_page + pmd_index(addr);

- if (!pmd_present(*pmd))
- set_pmd(pmd, __pmd(addr | pmd_flag));
+ if (pmd_present(*pmd))
+ continue;
+
+ set_pmd(pmd, __pmd((addr - info->offset) | info->pmd_flag));
}
}

@@ -30,13 +32,13 @@ static int ident_pud_init(struct x86_map

if (pud_present(*pud)) {
pmd = pmd_offset(pud, 0);
- ident_pmd_init(info->pmd_flag, pmd, addr, next);
+ ident_pmd_init(info, pmd, addr, next);
continue;
}
pmd = (pmd_t *)info->alloc_pgt_page(info->context);
if (!pmd)
return -ENOMEM;
- ident_pmd_init(info->pmd_flag, pmd, addr, next);
+ ident_pmd_init(info, pmd, addr, next);
set_pud(pud, __pud(__pa(pmd) | _KERNPG_TABLE));
}

@@ -44,14 +46,15 @@ static int ident_pud_init(struct x86_map
}

int kernel_ident_mapping_init(struct x86_mapping_info *info, pgd_t *pgd_page,
- unsigned long addr, unsigned long end)
+ unsigned long pstart, unsigned long pend)
{
+ unsigned long addr = pstart + info->offset;
+ unsigned long end = pend + info->offset;
unsigned long next;
int result;
- int off = info->kernel_mapping ? pgd_index(__PAGE_OFFSET) : 0;

for (; addr < end; addr = next) {
- pgd_t *pgd = pgd_page + pgd_index(addr) + off;
+ pgd_t *pgd = pgd_page + pgd_index(addr);
pud_t *pud;

next = (addr & PGDIR_MASK) + PGDIR_SIZE;
Index: linux-pm/arch/x86/power/hibernate_64.c
===================================================================
--- linux-pm.orig/arch/x86/power/hibernate_64.c
+++ linux-pm/arch/x86/power/hibernate_64.c
@@ -87,7 +87,7 @@ static int set_up_temporary_mappings(voi
struct x86_mapping_info info = {
.alloc_pgt_page = alloc_pgt_page,
.pmd_flag = __PAGE_KERNEL_LARGE_EXEC,
- .kernel_mapping = true,
+ .offset = __PAGE_OFFSET,
};
unsigned long mstart, mend;
pgd_t *pgd;
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