The following commit has been merged into the x86/mm branch of tip: Commit-ID: e9935b87c46236e8d7dd0acb847a31952db25228 Gitweb: https://git.kernel.org/tip/e9935b87c46236e8d7dd0acb847a31952db25228 Author: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> AuthorDate: Mon, 03 Oct 2022 13:23:46 -07:00 Committer: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> CommitterDate: Tue, 04 Oct 2022 11:00:24 -07:00 x86/mm: Ease W^X enforcement back to just a warning Currently, the "change_page_attr" (CPA) code refuses to create W+X mappings on 64-bit kernels. There have been reports both from 32-bit[1] and from BPF[2] users where this change kept the system from booting. These reports are showing up even after about a month of soak time in -next. To avoid breaking anything, never enforce W^X. Always warn and return the requested permissions even if a problem is detected. 1. https://lore.kernel.org/all/CAMj1kXHcF_iK_g0OZSkSv56Wmr=eQGQwNstcNjLEfS=mm7a06w@xxxxxxxxxxxxxx/ 2. https://lore.kernel.org/bpf/c84cc27c1a5031a003039748c3c099732a718aec.camel@xxxxxxxxxx/T/#u Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: Ingo Molnar <mingo@xxxxxxxxxx> Cc: Borislav Petkov <bp@xxxxxxxxx> Cc: x86@xxxxxxxxxx Cc: "H. Peter Anvin" <hpa@xxxxxxxxx> Cc: Kees Cook <keescook@xxxxxxxxxxxx> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> --- arch/x86/mm/pat/set_memory.c | 14 +++++++++----- 1 file changed, 9 insertions(+), 5 deletions(-) diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c index efe882c..97342c4 100644 --- a/arch/x86/mm/pat/set_memory.c +++ b/arch/x86/mm/pat/set_memory.c @@ -580,7 +580,7 @@ static inline pgprot_t static_protections(pgprot_t prot, unsigned long start, } /* - * Validate and enforce strict W^X semantics. + * Validate 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) @@ -595,7 +595,7 @@ static inline pgprot_t verify_rwx(pgprot_t old, pgprot_t new, unsigned long star if (IS_ENABLED(CONFIG_X86_32)) return new; - /* Only enforce when NX is supported: */ + /* Only verify when NX is supported: */ if (!(__supported_pte_mask & _PAGE_NX)) return new; @@ -606,13 +606,17 @@ static inline pgprot_t verify_rwx(pgprot_t old, pgprot_t new, unsigned long star return new; end = start + npg * PAGE_SIZE - 1; - WARN_ONCE(1, "CPA refuse W^X violation: %016llx -> %016llx range: 0x%016lx - 0x%016lx PFN %lx\n", + WARN_ONCE(1, "CPA detected 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; + /* + * For now, allow all permission change attempts by returning the + * attempted permissions. This can 'return old' to actively + * refuse the permission change at a later time. + */ + return new; } /*
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