4.16-stable review patch. If anyone has any objections, please let me know. ------------------ From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> [ 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@xxxxxxxxxxxxxxx> Acked-by: Kees Cook <keescook@xxxxxxxxxxxx> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx> Cc: Andy Lutomirski <luto@xxxxxxxxxx> Cc: Arjan van de Ven <arjan@xxxxxxxxxxxxxxx> Cc: Borislav Petkov <bp@xxxxxxxxx> Cc: Dan Williams <dan.j.williams@xxxxxxxxx> Cc: David Woodhouse <dwmw2@xxxxxxxxxxxxx> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> Cc: Hugh Dickins <hughd@xxxxxxxxxx> Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx> Cc: Juergen Gross <jgross@xxxxxxxx> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Cc: Nadav Amit <namit@xxxxxxxxxx> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: linux-mm@xxxxxxxxx Link: http://lkml.kernel.org/r/20180406205514.8D898241@xxxxxxxxxxxxxxxxxx Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx> Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- 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 @@ -298,9 +298,11 @@ 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;
