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The 'make rodata read-only' patch in -mm exposes a latent bug in the 32-bit change_page_attr() function, which causes certain CPUs (Those with NX basically) to reboot instantly after pages are marked read-only. The same bug got fixed a while back on x86-64, but never got propagated to i386. Stuart Hayes from Dell also picked up on this last June, but it never got fixed, as the only thing affected by it aparently was the nvidia driver. Blatantly stealing description from his post.. "It doesn't appear to be fixed (in the i386 arch). The change_page_attr()/split_large_page() code will still still set all the 4K PTEs to PAGE_KERNEL (setting the _PAGE_NX bit) when a large page needs to be split. This wouldn't be a problem for the bulk of the kernel memory, but there are pages in the lower 4MB of memory that's free, and are part of large executable pages that also contain kernel code. If change_page_attr() is called on these, it will set the _PAGE_NX bit on the whole 2MB region that was covered by the large page, causing a large chunk of kernel code to be non-executable." Signed-off-by: Arjan van de Ven <arjan@infradead.org> Signed-off-by: Dave Jones <davej@redhat.com> Cc: <Stuart_Hayes@Dell.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org> |
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