From: "Matthew Wilcox (Oracle)" willy@infradead.org
[ Upstream commit c1fcf41cf37f7a3fd3bbf6f0c04aba3ea4258888 ]
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@t... Closes: https://lore.kernel.org/oe-lkp/202502241646.719f4651-lkp@intel.com Signed-off-by: Sasha Levin sashal@kernel.org --- 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 95bc50a8541c6..24c74136acb33 100644 --- a/arch/x86/mm/pat/set_memory.c +++ b/arch/x86/mm/pat/set_memory.c @@ -2422,7 +2422,7 @@ 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 };
/* @@ -2509,7 +2509,7 @@ 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, };
@@ -2552,7 +2552,7 @@ 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, };