Messages in this thread Patch in this message | | | Date | Wed, 25 Apr 2018 02:08:02 -0700 | From | tip-bot for Dave Hansen <> | Subject | [tip:x86/pti] x86/pti: Reduce amount of kernel text allowed to be Global |
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Commit-ID: a44ca8f5a30c008b54d07b00eed4eae7f169fcd0 Gitweb: https://git.kernel.org/tip/a44ca8f5a30c008b54d07b00eed4eae7f169fcd0 Author: Dave Hansen <dave.hansen@linux.intel.com> AuthorDate: Fri, 20 Apr 2018 15:20:23 -0700 Committer: Thomas Gleixner <tglx@linutronix.de> CommitDate: Wed, 25 Apr 2018 11:02:50 +0200
x86/pti: Reduce amount of kernel text allowed to be Global
commit abb67605203687c8b7943d760638d0301787f8d9
Kees reported to me that I made too much of the kernel image global. It was far more than just text:
I think this is too much set global: _end is after data, bss, and brk, and all kinds of other stuff that could hold secrets. I think this should match what mark_rodata_ro() is doing.
This does exactly that. We use __end_rodata_hpage_align as our marker both because it is huge-page-aligned and it does not contain any sections we expect to hold secrets.
Kees's logic was that r/o data is in the kernel image anyway and, in the case of traditional distributions, can be freely downloaded from the web, so there's no reason to hide it.
Fixes: 8c06c7740 (x86/pti: Leave kernel text global for !PCID) Reported-by: Kees Cook <keescook@google.com> Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Acked-by: Ingo Molnar <mingo@kernel.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Juergen Gross <jgross@suse.com> Cc: Josh Poimboeuf <jpoimboe@redhat.com> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: David Woodhouse <dwmw2@infradead.org> Cc: Hugh Dickins <hughd@google.com> Cc: linux-mm@kvack.org Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Borislav Petkov <bp@alien8.de> Cc: Andy Lutomirski <luto@kernel.org> Cc: Nadav Amit <namit@vmware.com> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Arjan van de Ven <arjan@linux.intel.com> Link: https://lkml.kernel.org/r/20180420222023.1C8B2B20@viggo.jf.intel.com
--- arch/x86/mm/pti.c | 16 +++++++++++++--- 1 file changed, 13 insertions(+), 3 deletions(-)
diff --git a/arch/x86/mm/pti.c b/arch/x86/mm/pti.c index f1fd52f449e0..ae3eb4f5d53b 100644 --- a/arch/x86/mm/pti.c +++ b/arch/x86/mm/pti.c @@ -430,12 +430,24 @@ static inline bool pti_kernel_image_global_ok(void) */ void pti_clone_kernel_text(void) { + /* + * rodata is part of the kernel image and is normally + * readable on the filesystem or on the web. But, do not + * clone the areas past rodata, they might contain secrets. + */ unsigned long start = PFN_ALIGN(_text); - unsigned long end = ALIGN((unsigned long)_end, PMD_PAGE_SIZE); + unsigned long end = (unsigned long)__end_rodata_hpage_align; if (!pti_kernel_image_global_ok()) return; + pr_debug("mapping partial kernel image into user address space\n"); + + /* + * Note that this will undo _some_ of the work that + * pti_set_kernel_image_nonglobal() did to clear the + * global bit. + */ pti_clone_pmds(start, end, _PAGE_RW); } @@ -458,8 +470,6 @@ void pti_set_kernel_image_nonglobal(void) if (pti_kernel_image_global_ok()) return; - pr_debug("set kernel image non-global\n"); - set_memory_nonglobal(start, (end - start) >> PAGE_SHIFT); }
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