Messages in this thread | | | From | Kees Cook <> | Date | Fri, 30 Sep 2016 09:25:45 -0700 | Subject | Re: [PATCH 3/3] arm64: dump: Add checking for writable and exectuable pages |
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On Fri, Sep 30, 2016 at 8:58 AM, Mark Rutland <mark.rutland@arm.com> wrote: > On Thu, Sep 29, 2016 at 02:32:57PM -0700, Laura Abbott wrote: >> @@ -219,6 +223,15 @@ static void note_page(struct pg_state *st, unsigned long addr, unsigned level, >> unsigned long delta; >> >> if (st->current_prot) { >> + if (st->check_wx && >> + ((st->current_prot & PTE_RDONLY) != PTE_RDONLY) && >> + ((st->current_prot & PTE_PXN) != PTE_PXN)) { >> + WARN_ONCE(1, "arm64/mm: Found insecure W+X mapping at address %p/%pS\n", >> + (void *)st->start_address, >> + (void *)st->start_address); >> + st->wx_pages += (addr - st->start_address) / PAGE_SIZE; >> + } >> + > > Would it be worth verifying that all kernel mappings are UXN, too? > > ARMv8 allows execute-only mappings, and a !UXN mapping could result in an info > leak (e.g. pointers in MOVZ+MOVK sequences), or potential asynchronous issues > (e.g. user instruction fetches accessing read-destructive device registers). > All kernel mappings *should* be UXN.
I love this idea, but based on what came up with hardened usercopy, there are a lot of readers of kernel memory still. I think the expectations around UXN need to be clarified so we can reason about things like perf that want to read the kernel text.
-Kees
-- Kees Cook Nexus Security
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