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x86/mm: Ease W^X enforcement back to just a warning

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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@mail.gmail.com/
2. https://lore.kernel.org/bpf/c84cc27c1a5031a003039748c3c099732a718aec.camel@kernel.org/T/#u

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: x86@kernel.org
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Peter Zijlstra <peterz@infradead.org>
This commit is contained in:
Dave Hansen 2022-10-03 13:23:46 -07:00
parent 8c4934f475
commit c5129ecc12
1 changed files with 9 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

14
arch/x86/mm/pat/set_memory.c
View File

@ -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;
}
/*