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| author |   Matthew Wilcox (Oracle) <willy@infradead.org> | 2025-02-25 19:37:32 +0000 |
|---|---|---|
| committer |   Ingo Molnar <mingo@kernel.org> | 2025-02-27 09:58:17 +0100 |
| commit | c1fcf41cf37f7a3fd3bbf6f0c04aba3ea4258888 (patch) | |
| tree | bacee57e2e65f32d246b7b3a4803cba0c8a6325a | |
| parent | x86/mtrr: Remove unnecessary strlen() in mtrr_write() (diff) | |
| download | wireguard-linux-c1fcf41cf37f7a3fd3bbf6f0c04aba3ea4258888.tar.xz wireguard-linux-c1fcf41cf37f7a3fd3bbf6f0c04aba3ea4258888.zip | |
x86/mm: Clear _PAGE_DIRTY for kernel mappings when we clear _PAGE_RW
The bit pattern of _PAGE_DIRTY set and _PAGE_RW clear is used to mark
shadow stacks. This is currently checked for in mk_pte() but not
pfn_pte(). If we add the check to pfn_pte(), it catches vfree()
calling set_direct_map_invalid_noflush() which calls
__change_page_attr() which loads the old protection bits from the
PTE, clears the specified bits and uses pfn_pte() to construct the
new PTE.
We should, therefore, for kernel mappings, clear the _PAGE_DIRTY bit
consistently whenever we clear _PAGE_RW. I opted to do it in the
callers in case we want to use __change_page_attr() to create shadow
stacks inside the kernel at some point in the future. Arguably, we
might also want to clear _PAGE_ACCESSED here.
Note that the 3 functions involved:
__set_pages_np()
kernel_map_pages_in_pgd()
kernel_unmap_pages_in_pgd()
Only ever manipulate non-swappable kernel mappings, so maintaining
the DIRTY:1|RW:0 special pattern for shadow stacks and DIRTY:0
pattern for non-shadow-stack entries can be maintained consistently
and doesn't result in the unintended clearing of a live dirty bit
that could corrupt (destroy) dirty bit information for user mappings.
Reported-by: kernel test robot <oliver.sang@intel.com>
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/174051422675.10177.13226545170101706336.tip-bot2@tip-bot2
Closes: https://lore.kernel.org/oe-lkp/202502241646.719f4651-lkp@intel.com
| -rw-r--r-- | arch/x86/mm/pat/set_memory.c | 6 |
1 files changed, 3 insertions, 3 deletions
diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c index 84d0bca3be28..d1740159029e 100644 --- a/arch/x86/mm/pat/set_memory.c +++ b/arch/x86/mm/pat/set_memory.c @@ -2628,7 +2628,7 @@ static int __set_pages_np(struct page *page, int numpages) .pgd = NULL, .numpages = numpages, .mask_set = __pgprot(0), - .mask_clr = __pgprot(_PAGE_PRESENT | _PAGE_RW), + .mask_clr = __pgprot(_PAGE_PRESENT | _PAGE_RW | _PAGE_DIRTY), .flags = CPA_NO_CHECK_ALIAS }; /* @@ -2715,7 +2715,7 @@ int __init kernel_map_pages_in_pgd(pgd_t *pgd, u64 pfn, unsigned long address, .pgd = pgd, .numpages = numpages, .mask_set = __pgprot(0), - .mask_clr = __pgprot(~page_flags & (_PAGE_NX|_PAGE_RW)), + .mask_clr = __pgprot(~page_flags & (_PAGE_NX|_PAGE_RW|_PAGE_DIRTY)), .flags = CPA_NO_CHECK_ALIAS, }; @@ -2758,7 +2758,7 @@ int __init kernel_unmap_pages_in_pgd(pgd_t *pgd, unsigned long address, .pgd = pgd, .numpages = numpages, .mask_set = __pgprot(0), - .mask_clr = __pgprot(_PAGE_PRESENT | _PAGE_RW), + .mask_clr = __pgprot(_PAGE_PRESENT | _PAGE_RW | _PAGE_DIRTY), .flags = CPA_NO_CHECK_ALIAS, }; |