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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id md18sm108396pjb.9.2022.01.19.10.51.35 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 19 Jan 2022 10:51:35 -0800 (PST) Date: Wed, 19 Jan 2022 10:51:34 -0800 From: Kees Cook To: He Ying Subject: Re: [PATCH] powerpc/process, kasan: Silence KASAN warnings in __get_wchan() Message-ID: <202201191051.E49ED291@keescook> References: <20220119015025.136902-1-heying24@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220119015025.136902-1-heying24@huawei.com> X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: catalin.marinas@arm.com, linux-kernel@vger.kernel.org, sxwjean@gmail.com, peterz@infradead.org, paulus@samba.org, npiggin@gmail.com, linuxppc-dev@lists.ozlabs.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Tue, Jan 18, 2022 at 08:50:25PM -0500, He Ying wrote: > The following KASAN warning was reported in our kernel. > > BUG: KASAN: stack-out-of-bounds in get_wchan+0x188/0x250 > Read of size 4 at addr d216f958 by task ps/14437 > > CPU: 3 PID: 14437 Comm: ps Tainted: G O 5.10.0 #1 > Call Trace: > [daa63858] [c0654348] dump_stack+0x9c/0xe4 (unreliable) > [daa63888] [c035cf0c] print_address_description.constprop.3+0x8c/0x570 > [daa63908] [c035d6bc] kasan_report+0x1ac/0x218 > [daa63948] [c00496e8] get_wchan+0x188/0x250 > [daa63978] [c0461ec8] do_task_stat+0xce8/0xe60 > [daa63b98] [c0455ac8] proc_single_show+0x98/0x170 > [daa63bc8] [c03cab8c] seq_read_iter+0x1ec/0x900 > [daa63c38] [c03cb47c] seq_read+0x1dc/0x290 > [daa63d68] [c037fc94] vfs_read+0x164/0x510 > [daa63ea8] [c03808e4] ksys_read+0x144/0x1d0 > [daa63f38] [c005b1dc] ret_from_syscall+0x0/0x38 > --- interrupt: c00 at 0x8fa8f4 > LR = 0x8fa8cc > > The buggy address belongs to the page: > page:98ebcdd2 refcount:0 mapcount:0 mapping:00000000 index:0x2 pfn:0x1216f > flags: 0x0() > raw: 00000000 00000000 01010122 00000000 00000002 00000000 ffffffff 00000000 > raw: 00000000 > page dumped because: kasan: bad access detected > > Memory state around the buggy address: > d216f800: 00 00 00 00 00 f1 f1 f1 f1 00 00 00 00 00 00 00 > d216f880: f2 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 > >d216f900: 00 00 00 00 00 00 00 00 00 00 00 f1 f1 f1 f1 00 > ^ > d216f980: f2 f2 f2 f2 f2 f2 f2 00 00 00 00 00 00 00 00 00 > d216fa00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 > > After looking into this issue, I find the buggy address belongs > to the task stack region. It seems KASAN has something wrong. > I look into the code of __get_wchan in x86 architecture and > find the same issue has been resolved by the commit > f7d27c35ddff ("x86/mm, kasan: Silence KASAN warnings in get_wchan()"). > The solution could be applied to powerpc architecture too. > > As Andrey Ryabinin said, get_wchan() is racy by design, it may > access volatile stack of running task, thus it may access > redzone in a stack frame and cause KASAN to warn about this. > > Use READ_ONCE_NOCHECK() to silence these warnings. > > Signed-off-by: He Ying Looks reasonable to me; thanks! Reviewed-by: Kees Cook -Kees > --- > arch/powerpc/kernel/process.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c > index 984813a4d5dc..a75d20f23dac 100644 > --- a/arch/powerpc/kernel/process.c > +++ b/arch/powerpc/kernel/process.c > @@ -2160,12 +2160,12 @@ static unsigned long ___get_wchan(struct task_struct *p) > return 0; > > do { > - sp = *(unsigned long *)sp; > + sp = READ_ONCE_NOCHECK(*(unsigned long *)sp); > if (!validate_sp(sp, p, STACK_FRAME_OVERHEAD) || > task_is_running(p)) > return 0; > if (count > 0) { > - ip = ((unsigned long *)sp)[STACK_FRAME_LR_SAVE]; > + ip = READ_ONCE_NOCHECK(((unsigned long *)sp)[STACK_FRAME_LR_SAVE]); > if (!in_sched_functions(ip)) > return ip; > } > -- > 2.17.1 > -- Kees Cook