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Date: Thu, 25 Aug 2022 14:23:31 +0200 From: Peter Zijlstra <peterz@...radead.org> To: Dave Hansen <dave.hansen@...el.com>, x86@...nel.org Cc: linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org, keescook@...omium.org Subject: [PATCH] x86/mm: Refuse W^X violations x86 has STRICT_*_RWX, but not even a warning when someone violates it. Add this warning and fully refuse the transition. Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org> --- diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c index 1abd5438f126..9e9bef3f36b3 100644 --- a/arch/x86/mm/pat/set_memory.c +++ b/arch/x86/mm/pat/set_memory.c @@ -579,6 +579,30 @@ static inline pgprot_t static_protections(pgprot_t prot, unsigned long start, return __pgprot(pgprot_val(prot) & ~forbidden); } +/* + * Validate and enforce strict W^X semantics. + */ +static inline pgprot_t verify_rwx(pgprot_t old, pgprot_t new, unsigned long start, + unsigned long pfn, unsigned long npg) +{ + unsigned long end; + + if (!((pgprot_val(old) ^ pgprot_val(new)) & (_PAGE_RW | _PAGE_NX))) + return new; + + if ((pgprot_val(new) & (_PAGE_RW | _PAGE_NX)) != _PAGE_RW) + return new; + + end = start + npg * PAGE_SIZE - 1; + WARN(1, "CPA refuse W^X violation: %016llx -> %016llx range: 0x%016lx - 0x%016lx PFN %lx\n", + (unsigned long long)pgprot_val(old), + (unsigned long long)pgprot_val(new), + start, end, pfn); + + /* refuse the transition into WX */ + return old; +} + /* * Lookup the page table entry for a virtual address in a specific pgd. * Return a pointer to the entry and the level of the mapping. @@ -885,6 +909,8 @@ static int __should_split_large_page(pte_t *kpte, unsigned long address, new_prot = static_protections(req_prot, lpaddr, old_pfn, numpages, psize, CPA_DETECT); + new_prot = verify_rwx(old_prot, new_prot, lpaddr, old_pfn, numpages); + /* * If there is a conflict, split the large page. * @@ -1525,6 +1551,7 @@ static int __change_page_attr(struct cpa_data *cpa, int primary) if (level == PG_LEVEL_4K) { pte_t new_pte; + pgprot_t old_prot = pte_pgprot(old_pte); pgprot_t new_prot = pte_pgprot(old_pte); unsigned long pfn = pte_pfn(old_pte); @@ -1536,6 +1563,8 @@ static int __change_page_attr(struct cpa_data *cpa, int primary) new_prot = static_protections(new_prot, address, pfn, 1, 0, CPA_PROTECT); + new_prot = verify_rwx(old_prot, new_prot, address, pfn, 1); + new_prot = pgprot_clear_protnone_bits(new_prot); /*
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