From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andy Shevchenko Subject: Re: [PATCH] vsprintf: Do not break early boot with probing addresses Date: Thu, 9 May 2019 16:05:12 +0300 Message-ID: <20190509130512.GS9224@smile.fi.intel.com> References: <20190509121923.8339-1-pmladek@suse.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20190509121923.8339-1-pmladek@suse.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: linuxppc-dev-bounces+glppe-linuxppc-embedded-2=m.gmane.org@lists.ozlabs.org Sender: "Linuxppc-dev" To: Petr Mladek Cc: linux-arch@vger.kernel.org, Sergey Senozhatsky , Heiko Carstens , linux-s390@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, Rasmus Villemoes , linux-kernel@vger.kernel.org, Steven Rostedt , Michal Hocko , Sergey Senozhatsky , Stephen Rothwell , Linus Torvalds , Martin Schwidefsky , "Tobin C . Harding" List-Id: linux-arch.vger.kernel.org On Thu, May 09, 2019 at 02:19:23PM +0200, Petr Mladek wrote: > The commit 3e5903eb9cff70730 ("vsprintf: Prevent crash when dereferencing > invalid pointers") broke boot on several architectures. The common > pattern is that probe_kernel_read() is not working during early > boot because userspace access framework is not ready. > > The check is only the best effort. Let's not rush with it during > the early boot. > > Details: > > 1. Report on Power: > > Kernel crashes very early during boot with with CONFIG_PPC_KUAP and > CONFIG_JUMP_LABEL_FEATURE_CHECK_DEBUG > > The problem is the combination of some new code called via printk(), > check_pointer() which calls probe_kernel_read(). That then calls > allow_user_access() (PPC_KUAP) and that uses mmu_has_feature() too early > (before we've patched features). With the JUMP_LABEL debug enabled that > causes us to call printk() & dump_stack() and we end up recursing and > overflowing the stack. > > Because it happens so early you don't get any output, just an apparently > dead system. > > The stack trace (which you don't see) is something like: > > ... > dump_stack+0xdc > probe_kernel_read+0x1a4 > check_pointer+0x58 > string+0x3c > vsnprintf+0x1bc > vscnprintf+0x20 > printk_safe_log_store+0x7c > printk+0x40 > dump_stack_print_info+0xbc > dump_stack+0x8 > probe_kernel_read+0x1a4 > probe_kernel_read+0x19c > check_pointer+0x58 > string+0x3c > vsnprintf+0x1bc > vscnprintf+0x20 > vprintk_store+0x6c > vprintk_emit+0xec > vprintk_func+0xd4 > printk+0x40 > cpufeatures_process_feature+0xc8 > scan_cpufeatures_subnodes+0x380 > of_scan_flat_dt_subnodes+0xb4 > dt_cpu_ftrs_scan_callback+0x158 > of_scan_flat_dt+0xf0 > dt_cpu_ftrs_scan+0x3c > early_init_devtree+0x360 > early_setup+0x9c > > 2. Report on s390: > > vsnprintf invocations, are broken on s390. For example, the early boot > output now looks like this where the first (efault) should be > the linux_banner: > > [ 0.099985] (efault) > [ 0.099985] setup: Linux is running as a z/VM guest operating system in 64-bit mode > [ 0.100066] setup: The maximum memory size is 8192MB > [ 0.100070] cma: Reserved 4 MiB at (efault) > [ 0.100100] numa: NUMA mode: (efault) > > The reason for this, is that the code assumes that > probe_kernel_address() works very early. This however is not true on > at least s390. Uaccess on KERNEL_DS works only after page tables have > been setup on s390, which happens with setup_arch()->paging_init(). > > Any probe_kernel_address() invocation before that will return -EFAULT. > It's seems as a good enough fix. Reviewed-by: Andy Shevchenko Though in all cases would be nice to distinguish error pointers as well. Something like if (IS_ERR(ptr)) return err_pointer_str(ptr); in check_pointer_msg(). > Fixes: 3e5903eb9cff70730 ("vsprintf: Prevent crash when dereferencing invalid pointers") > Signed-off-by: Petr Mladek > --- > lib/vsprintf.c | 9 +++++++-- > 1 file changed, 7 insertions(+), 2 deletions(-) > > diff --git a/lib/vsprintf.c b/lib/vsprintf.c > index 7b0a6140bfad..8b43a883be6b 100644 > --- a/lib/vsprintf.c > +++ b/lib/vsprintf.c > @@ -640,8 +640,13 @@ static const char *check_pointer_msg(const void *ptr) > if (!ptr) > return "(null)"; > > - if (probe_kernel_address(ptr, byte)) > - return "(efault)"; > + /* User space address handling is not ready during early boot. */ > + if (system_state <= SYSTEM_BOOTING) { > + if ((unsigned long)ptr < PAGE_SIZE) > + return "(efault)"; > + } else { > + if (probe_kernel_address(ptr, byte)) > + return "(efault)"; > > return NULL; > } > -- > 2.16.4 > -- With Best Regards, Andy Shevchenko From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mga02.intel.com ([134.134.136.20]:37976 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726583AbfEINKV (ORCPT ); Thu, 9 May 2019 09:10:21 -0400 Date: Thu, 9 May 2019 16:05:12 +0300 From: Andy Shevchenko Subject: Re: [PATCH] vsprintf: Do not break early boot with probing addresses Message-ID: <20190509130512.GS9224@smile.fi.intel.com> References: <20190509121923.8339-1-pmladek@suse.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190509121923.8339-1-pmladek@suse.com> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Petr Mladek Cc: Linus Torvalds , Rasmus Villemoes , "Tobin C . Harding" , Michal Hocko , Sergey Senozhatsky , Steven Rostedt , Sergey Senozhatsky , linux-kernel@vger.kernel.org, Michael Ellerman , linuxppc-dev@lists.ozlabs.org, Russell Currey , Christophe Leroy , Stephen Rothwell , Heiko Carstens , linux-arch@vger.kernel.org, linux-s390@vger.kernel.org, Martin Schwidefsky Message-ID: <20190509130512.eOpTHWX1Vw219J1juYw-SpeQRpBzQZT5CGSN2gh29i4@z> On Thu, May 09, 2019 at 02:19:23PM +0200, Petr Mladek wrote: > The commit 3e5903eb9cff70730 ("vsprintf: Prevent crash when dereferencing > invalid pointers") broke boot on several architectures. The common > pattern is that probe_kernel_read() is not working during early > boot because userspace access framework is not ready. > > The check is only the best effort. Let's not rush with it during > the early boot. > > Details: > > 1. Report on Power: > > Kernel crashes very early during boot with with CONFIG_PPC_KUAP and > CONFIG_JUMP_LABEL_FEATURE_CHECK_DEBUG > > The problem is the combination of some new code called via printk(), > check_pointer() which calls probe_kernel_read(). That then calls > allow_user_access() (PPC_KUAP) and that uses mmu_has_feature() too early > (before we've patched features). With the JUMP_LABEL debug enabled that > causes us to call printk() & dump_stack() and we end up recursing and > overflowing the stack. > > Because it happens so early you don't get any output, just an apparently > dead system. > > The stack trace (which you don't see) is something like: > > ... > dump_stack+0xdc > probe_kernel_read+0x1a4 > check_pointer+0x58 > string+0x3c > vsnprintf+0x1bc > vscnprintf+0x20 > printk_safe_log_store+0x7c > printk+0x40 > dump_stack_print_info+0xbc > dump_stack+0x8 > probe_kernel_read+0x1a4 > probe_kernel_read+0x19c > check_pointer+0x58 > string+0x3c > vsnprintf+0x1bc > vscnprintf+0x20 > vprintk_store+0x6c > vprintk_emit+0xec > vprintk_func+0xd4 > printk+0x40 > cpufeatures_process_feature+0xc8 > scan_cpufeatures_subnodes+0x380 > of_scan_flat_dt_subnodes+0xb4 > dt_cpu_ftrs_scan_callback+0x158 > of_scan_flat_dt+0xf0 > dt_cpu_ftrs_scan+0x3c > early_init_devtree+0x360 > early_setup+0x9c > > 2. Report on s390: > > vsnprintf invocations, are broken on s390. For example, the early boot > output now looks like this where the first (efault) should be > the linux_banner: > > [ 0.099985] (efault) > [ 0.099985] setup: Linux is running as a z/VM guest operating system in 64-bit mode > [ 0.100066] setup: The maximum memory size is 8192MB > [ 0.100070] cma: Reserved 4 MiB at (efault) > [ 0.100100] numa: NUMA mode: (efault) > > The reason for this, is that the code assumes that > probe_kernel_address() works very early. This however is not true on > at least s390. Uaccess on KERNEL_DS works only after page tables have > been setup on s390, which happens with setup_arch()->paging_init(). > > Any probe_kernel_address() invocation before that will return -EFAULT. > It's seems as a good enough fix. Reviewed-by: Andy Shevchenko Though in all cases would be nice to distinguish error pointers as well. Something like if (IS_ERR(ptr)) return err_pointer_str(ptr); in check_pointer_msg(). > Fixes: 3e5903eb9cff70730 ("vsprintf: Prevent crash when dereferencing invalid pointers") > Signed-off-by: Petr Mladek > --- > lib/vsprintf.c | 9 +++++++-- > 1 file changed, 7 insertions(+), 2 deletions(-) > > diff --git a/lib/vsprintf.c b/lib/vsprintf.c > index 7b0a6140bfad..8b43a883be6b 100644 > --- a/lib/vsprintf.c > +++ b/lib/vsprintf.c > @@ -640,8 +640,13 @@ static const char *check_pointer_msg(const void *ptr) > if (!ptr) > return "(null)"; > > - if (probe_kernel_address(ptr, byte)) > - return "(efault)"; > + /* User space address handling is not ready during early boot. */ > + if (system_state <= SYSTEM_BOOTING) { > + if ((unsigned long)ptr < PAGE_SIZE) > + return "(efault)"; > + } else { > + if (probe_kernel_address(ptr, byte)) > + return "(efault)"; > > return NULL; > } > -- > 2.16.4 > -- With Best Regards, Andy Shevchenko