The following commit has been merged into the x86/mm branch of tip: Commit-ID: d75a256b6a64132fc7aab57ad4c96218e3ae383b Gitweb: https://git.kernel.org/tip/d75a256b6a64132fc7aab57ad4c96218e3ae383b Author: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx> AuthorDate: Tue, 25 Feb 2025 19:37:32 Committer: Ingo Molnar <mingo@xxxxxxxxxx> CommitterDate: Tue, 25 Feb 2025 20:59:32 +01:00 x86/mm: Clear _PAGE_DIRTY 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, clear the _PAGE_DIRTY bit 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. Reported-by: kernel test robot <oliver.sang@xxxxxxxxx> Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx> Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Closes: https://lore.kernel.org/oe-lkp/202502241646.719f4651-lkp@xxxxxxxxx --- arch/x86/mm/pat/set_memory.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c index 84d0bca..d174015 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, };
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