From: Kirill A. Shutemov Date: Wed, 16 Oct 2024 11:14:55 +0000 (+0300) Subject: x86/mm/ident_map: Fix theoretical virtual address overflow to zero X-Git-Tag: v6.15-rc1~216^2~58 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=f666c92090a41ac5524dade63ff96b3adcf8c2ab;p=thirdparty%2Fkernel%2Flinux.git x86/mm/ident_map: Fix theoretical virtual address overflow to zero The current calculation of the 'next' virtual address in the page table initialization functions in arch/x86/mm/ident_map.c doesn't protect against wrapping to zero. This is a theoretical issue that cannot happen currently, the problematic case is possible only if the user sets a high enough x86_mapping_info::offset value - which no current code in the upstream kernel does. ( The wrapping to zero only occurs if the top PGD entry is accessed. There are no such users upstream. Only hibernate_64.c uses x86_mapping_info::offset, and it operates on the direct mapping range, which is not the top PGD entry. ) Should such an overflow happen, it can result in page table corruption and a hang. To future-proof this code, replace the manual 'next' calculation with p?d_addr_end() which handles wrapping correctly. [ Backporter's note: there's no need to backport this patch. ] Signed-off-by: Kirill A. Shutemov Signed-off-by: Ingo Molnar Reviewed-by: Kai Huang Reviewed-by: Tom Lendacky Cc: Andy Lutomirski Cc: Linus Torvalds Link: https://lore.kernel.org/r/20241016111458.846228-2-kirill.shutemov@linux.intel.com --- diff --git a/arch/x86/mm/ident_map.c b/arch/x86/mm/ident_map.c index 5ab7bd2f1983c..bd5d101c5c379 100644 --- a/arch/x86/mm/ident_map.c +++ b/arch/x86/mm/ident_map.c @@ -101,9 +101,7 @@ static int ident_pud_init(struct x86_mapping_info *info, pud_t *pud_page, pmd_t *pmd; bool use_gbpage; - next = (addr & PUD_MASK) + PUD_SIZE; - if (next > end) - next = end; + next = pud_addr_end(addr, end); /* if this is already a gbpage, this portion is already mapped */ if (pud_leaf(*pud)) @@ -154,10 +152,7 @@ static int ident_p4d_init(struct x86_mapping_info *info, p4d_t *p4d_page, p4d_t *p4d = p4d_page + p4d_index(addr); pud_t *pud; - next = (addr & P4D_MASK) + P4D_SIZE; - if (next > end) - next = end; - + next = p4d_addr_end(addr, end); if (p4d_present(*p4d)) { pud = pud_offset(p4d, 0); result = ident_pud_init(info, pud, addr, next); @@ -199,10 +194,7 @@ int kernel_ident_mapping_init(struct x86_mapping_info *info, pgd_t *pgd_page, pgd_t *pgd = pgd_page + pgd_index(addr); p4d_t *p4d; - next = (addr & PGDIR_MASK) + PGDIR_SIZE; - if (next > end) - next = end; - + next = pgd_addr_end(addr, end); if (pgd_present(*pgd)) { p4d = p4d_offset(pgd, 0); result = ident_p4d_init(info, p4d, addr, next);