Date: Sat, 3 Dec 2016 10:11:21 +0100 From: Greg KH <gregkh@...uxfoundation.org> To: Kees Cook <keescook@...omium.org> Cc: Michael Ellerman <mpe@...erman.id.au>, "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, LKML <linux-kernel@...r.kernel.org> Subject: Re: [PATCH v2] lkdtm: Add tests for LIST_POISON and ZERO_SIZE_PTR On Sat, Dec 03, 2016 at 10:10:57AM +0100, Greg KH wrote: > On Fri, Dec 02, 2016 at 01:32:24PM -0800, Kees Cook wrote: > > On Thu, Dec 1, 2016 at 8:22 PM, Michael Ellerman <mpe@...erman.id.au> wrote: > > > This adds two tests, to check that a read or write to LIST_POISON1 and > > > ZERO_SIZE_PTR are blocked. > > > > > > The default values for both (256 and 16) typically fall in the range > > > of valid user space addresses. However in general mmap_min_addr is 64K, > > > which prevents user space from mapping anything at those addresses. > > > > > > However it's feasible that an attacker will be able to find a way to > > > cause an access at an offset from either value, and if that offset is > > > greater than 64K then they can access user space again. > > > > > > To simulate that case, in the test we create a user mapping at > > > approximately mmap_min_addr, and offset the pointer by that amount. This > > > gives the test the greatest chance of failing (ie. an access > > > succeeding). We don't actually use mmap_min_addr, because that would > > > require exporting it to modules, instead we use the default value at > > > compile time as a reasonable approximation. > > > > > > Signed-off-by: Michael Ellerman <mpe@...erman.id.au> > > > > Thanks for this! I like it. :) > > > > Acked-by: Kees Cook <keescook@...omium.org> > > > > Greg, can you take this into your tree? > > Sure, will do so on Monday. Oops, no, I will not, kbuild reports build errors with it :(
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