4.9-stable review patch. If anyone has any objections, please let me know.
------------------
From: Dave Hansen dave.hansen@linux.intel.com
[ Upstream commit 639d6aafe437a7464399d2a77d006049053df06f ]
__ro_after_init data gets stuck in the .rodata section. That's normally fine because the kernel itself manages the R/W properties.
But, if we run __change_page_attr() on an area which is __ro_after_init, the .rodata checks will trigger and force the area to be immediately read-only, even if it is early-ish in boot. This caused problems when trying to clear the _PAGE_GLOBAL bit for these area in the PTI code: it cleared _PAGE_GLOBAL like I asked, but also took it up on itself to clear _PAGE_RW. The kernel then oopses the next time it wrote to a __ro_after_init data structure.
To fix this, add the kernel_set_to_readonly check, just like we have for kernel text, just a few lines below in this function.
Signed-off-by: Dave Hansen dave.hansen@linux.intel.com Acked-by: Kees Cook keescook@chromium.org Cc: Andrea Arcangeli aarcange@redhat.com Cc: Andy Lutomirski luto@kernel.org Cc: Arjan van de Ven arjan@linux.intel.com Cc: Borislav Petkov bp@alien8.de Cc: Dan Williams dan.j.williams@intel.com Cc: David Woodhouse dwmw2@infradead.org Cc: Greg Kroah-Hartman gregkh@linuxfoundation.org Cc: Hugh Dickins hughd@google.com Cc: Josh Poimboeuf jpoimboe@redhat.com Cc: Juergen Gross jgross@suse.com Cc: Linus Torvalds torvalds@linux-foundation.org Cc: Nadav Amit namit@vmware.com Cc: Peter Zijlstra peterz@infradead.org Cc: Thomas Gleixner tglx@linutronix.de Cc: linux-mm@kvack.org Link: http://lkml.kernel.org/r/20180406205514.8D898241@viggo.jf.intel.com Signed-off-by: Ingo Molnar mingo@kernel.org Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/mm/pageattr.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)
--- a/arch/x86/mm/pageattr.c +++ b/arch/x86/mm/pageattr.c @@ -279,9 +279,11 @@ static inline pgprot_t static_protection
/* * The .rodata section needs to be read-only. Using the pfn - * catches all aliases. + * catches all aliases. This also includes __ro_after_init, + * so do not enforce until kernel_set_to_readonly is true. */ - if (within(pfn, __pa_symbol(__start_rodata) >> PAGE_SHIFT, + if (kernel_set_to_readonly && + within(pfn, __pa_symbol(__start_rodata) >> PAGE_SHIFT, __pa_symbol(__end_rodata) >> PAGE_SHIFT)) pgprot_val(forbidden) |= _PAGE_RW;