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Peter Anvin" , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: x86: pgtable / kaslr initialisation (OOB) help Message-ID: <20230614151003.GY3635807@google.com> References: <20230614132339.GS3635807@google.com> <20230614141654.GA1640123@hirez.programming.kicks-ass.net> <20230614143732.GW3635807@google.com> <0cefb67a-6fae-daa2-c871-ae35b96aac08@intel.com> <20230614150615.GX3635807@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20230614150615.GX3635807@google.com> X-Rspamd-Queue-Id: DA26F1C0028 X-Rspam-User: X-Stat-Signature: emf61dnwowqiwtns9ykdbbqm6h6tacc3 X-Rspamd-Server: rspam03 X-HE-Tag: 1686755410-453312 X-HE-Meta: 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 W8EbFXak xaBCAM2blTS18RBJGSJL9HH2sRQhp8pRxOyg4aw8v81Y+RDhpikOKJQtQ4LZayh4JudKc6PztzBLsoPYSMPyKat7HZfv/NNXcfXvWKMhtfNrZZxzL+CHc+PH85pmQXe/7H8OkJYRxlvGqbPVJmJyv/b+eOIDOaLB8NZr0rfqtAoUEgtMc+Mny5Jj64byR0cN6M/Fwx+ANbA1KSj2vLVKSa9f2CHgyivpxtvSwkXq6r1ewbta1gkrkR0d7It6Smfvnqgow X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, 14 Jun 2023, Lee Jones wrote: > Thanks for chiming in Dave. I hoped you would. > > On Wed, 14 Jun 2023, Dave Hansen wrote: > > > On 6/14/23 07:37, Lee Jones wrote: > > > Still unsure how we (the kernel) can/should write to an area of memory > > > that does not belong to it. Should we allocate enough memory > > > (2*PAGE_SIZE? rather than 8-Bytes) for trampoline_pgd_entry to consume > > > in a more sane way? > > > > No. > > > > I think this: > > > > set_pgd(&trampoline_pgd_entry, > > __pgd(_KERNPG_TABLE | __pa(p4d_page_tramp))); > > > > is bogus-ish. set_pgd() wants to operate on a pgd_t inside a pgd > > *PAGE*. But it's just being pointed at a single _entry_. The address > > of 'trampoline_pgd_entry' in your case also just (unfortunately) > > happens to pass the: > > > > __pti_set_user_pgtbl -> pgdp_maps_userspace() > > > > test. I _think_ we want these to just be something like: > > > > trampoline_pgd_entry = __pgd(_KERNPG_TABLE | > > __pa(p4d_page_tramp); > > > > That'll keep us away from all of the set_pgd()-induced nastiness. > > Okay. Is this what you're suggesting? > > diff --git a/arch/x86/mm/kaslr.c b/arch/x86/mm/kaslr.c v > index d336bb0cb38b..803595c7dcc8 100644 > --- a/arch/x86/mm/kaslr.c > +++ b/arch/x86/mm/kaslr.c > @@ -176,7 +176,7 @@ void __meminit init_trampoline_kaslr(void) > set_pgd(&trampoline_pgd_entry, > __pgd(_KERNPG_TABLE | __pa(p4d_page_tramp))); > } else { > - set_pgd(&trampoline_pgd_entry, > - __pgd(_KERNPG_TABLE | __pa(pud_page_tramp))); > + trampoline_pgd_entry = > + __pgd(_KERNPG_TABLE | __pa(p4d_page_tramp); Note the change of *.page_tramp here. s/pud/p4d/ I'm assuming that too was intentional? > } > } > > If so, I'll take it for a spin right now. -- Lee Jones [李琼斯]