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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id cx4sm4258976pjb.53.2021.07.13.20.10.02 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 13 Jul 2021 20:10:02 -0700 (PDT) Date: Tue, 13 Jul 2021 20:10:01 -0700 From: Kees Cook To: Sergei Trofimovich Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Alexander Potapenko , Thomas Gleixner , Vlastimil Babka , bowsingbetee@pm.me Subject: Re: [PATCH] mm: page_alloc: fix page_poison=1 / INIT_ON_ALLOC_DEFAULT_ON interaction Message-ID: <202107131953.BB3627156@keescook> References: <20210712005732.4f9bfa78@zn3> <20210712215816.1512739-1-slyfox@gentoo.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210712215816.1512739-1-slyfox@gentoo.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jul 12, 2021 at 10:58:16PM +0100, Sergei Trofimovich wrote: > To reproduce the failure we need the following system: > - kernel command: page_poison=1 init_on_free=0 init_on_alloc=0 > - kernel config: > * CONFIG_INIT_ON_ALLOC_DEFAULT_ON=y > * CONFIG_INIT_ON_FREE_DEFAULT_ON=y > * CONFIG_PAGE_POISONING=y > > 0000000085629bdd: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ > 0000000022861832: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ > 00000000c597f5b0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ > CPU: 11 PID: 15195 Comm: bash Kdump: loaded Tainted: G U O 5.13.1-gentoo-x86_64 #1 > Hardware name: System manufacturer System Product Name/PRIME Z370-A, BIOS 2801 01/13/2021 > Call Trace: > dump_stack+0x64/0x7c > __kernel_unpoison_pages.cold+0x48/0x84 > post_alloc_hook+0x60/0xa0 > get_page_from_freelist+0xdb8/0x1000 > __alloc_pages+0x163/0x2b0 > __get_free_pages+0xc/0x30 > pgd_alloc+0x2e/0x1a0 > ? dup_mm+0x37/0x4f0 > mm_init+0x185/0x270 > dup_mm+0x6b/0x4f0 > ? __lock_task_sighand+0x35/0x70 > copy_process+0x190d/0x1b10 > kernel_clone+0xba/0x3b0 > __do_sys_clone+0x8f/0xb0 > do_syscall_64+0x68/0x80 > ? do_syscall_64+0x11/0x80 > entry_SYSCALL_64_after_hwframe+0x44/0xae > > Before the 51cba1eb ("init_on_alloc: Optimize static branches") > init_on_alloc never enabled static branch by default. It could > only be enabed explicitly by init_mem_debugging_and_hardening(). But init_mem_debugging_and_hardening() is always called (by mm_init()). > But after the 51cba1eb static branch could already be enabled > by default. There was no code to ever disable it. That caused > page_poison=1 / init_on_free=1 conflict. > > This change extends init_mem_debugging_and_hardening() to also > disable static branch disabling. > > CC: Andrew Morton > CC: Kees Cook > CC: Alexander Potapenko > CC: Thomas Gleixner > CC: Vlastimil Babka > CC: linux-mm@kvack.org > Reported-by: bowsingbetee@pm.me > Reported-by: Mikhail Morfikov > Fixes: 51cba1eb ("init_on_alloc: Optimize static branches") > Signed-off-by: Sergei Trofimovich > --- > mm/page_alloc.c | 16 ++++++++++------ > 1 file changed, 10 insertions(+), 6 deletions(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 3b97e17806be..46cb4a9c2b50 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -840,18 +840,22 @@ void init_mem_debugging_and_hardening(void) > } > #endif > > - if (_init_on_alloc_enabled_early) { > - if (page_poisoning_requested) > + if (_init_on_alloc_enabled_early || > + IS_ENABLED(CONFIG_INIT_ON_ALLOC_DEFAULT_ON)) { This doesn't look right. _init_on_alloc_enabled_early already has the same value: static bool _init_on_alloc_enabled_early __read_mostly = IS_ENABLED(CONFIG_INIT_ON_ALLOC_DEFAULT_ON); So checking this is just a side-effect of how static_branch_maybe() happens to be behaving. > + if (page_poisoning_requested) { > pr_info("mem auto-init: CONFIG_PAGE_POISONING is on, " > "will take precedence over init_on_alloc\n"); > - else > + static_branch_disable(&init_on_alloc); > + } else > static_branch_enable(&init_on_alloc); > } > - if (_init_on_free_enabled_early) { > - if (page_poisoning_requested) > + if (_init_on_free_enabled_early || > + IS_ENABLED(CONFIG_INIT_ON_FREE_DEFAULT_ON)) { > + if (page_poisoning_requested) { > pr_info("mem auto-init: CONFIG_PAGE_POISONING is on, " > "will take precedence over init_on_free\n"); > - else > + static_branch_disable(&init_on_free); > + } else > static_branch_enable(&init_on_free); > } I think it would be better to clean this up without additional confusion involving the CONFIGs: diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 3b97e17806be..1f19365bc158 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -840,21 +840,24 @@ void init_mem_debugging_and_hardening(void) } #endif - if (_init_on_alloc_enabled_early) { - if (page_poisoning_requested) - pr_info("mem auto-init: CONFIG_PAGE_POISONING is on, " - "will take precedence over init_on_alloc\n"); - else - static_branch_enable(&init_on_alloc); - } - if (_init_on_free_enabled_early) { - if (page_poisoning_requested) - pr_info("mem auto-init: CONFIG_PAGE_POISONING is on, " - "will take precedence over init_on_free\n"); - else - static_branch_enable(&init_on_free); + if ((_init_on_alloc_enabled_early || _init_on_free_enabled_early) && + page_poisoning_requested) { + pr_info("mem auto-init: CONFIG_PAGE_POISONING is on, " + "will take precedence over init_on_alloc and init_on_free\n"); + _init_on_alloc_enabled_early = false; + _init_on_free_enabled_early = false; } + if (_init_on_alloc_enabled_early) + static_branch_enable(&init_on_alloc); + else + static_branch_disable(&init_on_alloc); + + if (_init_on_free_enabled_early) + static_branch_enable(&init_on_free); + else + static_branch_disable(&init_on_free); + #ifdef CONFIG_DEBUG_PAGEALLOC if (!debug_pagealloc_enabled()) return; -- Kees Cook