Date: Thu, 21 Jul 2016 22:34:33 -0700 From: Andy Lutomirski <luto@...nel.org> To: Valdis.Kletnieks@...edu, kernel-hardening@...ts.openwall.com Cc: x86@...nel.org, linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org, Borislav Petkov <bp@...en8.de>, Nadav Amit <nadav.amit@...il.com>, Kees Cook <keescook@...omium.org>, Brian Gerst <brgerst@...il.com>, Linus Torvalds <torvalds@...ux-foundation.org>, Josh Poimboeuf <jpoimboe@...hat.com>, Jann Horn <jann@...jh.net>, Heiko Carstens <heiko.carstens@...ibm.com> Subject: Re: [PATCH v5 03/32] x86/cpa: In populate_pgd, don't set the pgd entry until it's populated On 07/21/2016 09:43 PM, Valdis.Kletnieks@...edu wrote: > On Mon, 11 Jul 2016 13:53:36 -0700, Andy Lutomirski said: >> This avoids pointless races in which another CPU or task might see a >> partially populated global pgd entry. These races should normally >> be harmless, but, if another CPU propagates the entry via >> vmalloc_fault and then populate_pgd fails (due to memory allocation >> failure, for example), this prevents a use-after-free of the pgd >> entry. >> >> Signed-off-by: Andy Lutomirski <luto@...nel.org> >> --- >> arch/x86/mm/pageattr.c | 9 ++++++--- >> 1 file changed, 6 insertions(+), 3 deletions(-) > > I just bisected a failure to boot down to this patch. On my Dell Latitude > laptop, it results in the kernel being loaded and then just basically sitting > there dead in the water - as far as I can tell, it dies before the kernel > ever gets going far enough to do any console I/O (even with ignore_loglevel). > Nothing in /sys/fs/pstore either. I admit not understanding the VM code > at all, so I don't have a clue *why* this causes indigestion... > > CPU is an Intel Core i5-3340M in case that matters.... > How much memory do you have and what's your config? My code is obviously buggy, but I'm wondering why neither I nor the 0day bot caught this. The attached patch is compile-tested only. (Even Thunderbird doesn't want to send non-flowed text right now, sigh.) --Andy View attachment "0001-x86-mm-Fix-populate_pgd.patch" of type "text/x-patch" (3464 bytes)
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