From mboxrd@z Thu Jan 1 00:00:00 1970 From: Leonard Crestez Subject: Re: [PATCH v10 2/3] arm/syscalls: Check address limit on user-mode return Date: Tue, 18 Jul 2017 17:36:06 +0300 Message-ID: <1500388566.11612.74.camel@nxp.com> References: <20170615011203.144108-1-thgarnie@google.com> <20170615011203.144108-2-thgarnie@google.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: <20170615011203.144108-2-thgarnie-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org> Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Thomas Garnier , Thomas Gleixner , Ingo Molnar , "H . Peter Anvin" , Andy Lutomirski , Paolo Bonzini , Rik van Riel , Oleg Nesterov , Josh Poimboeuf , Petr Mladek , Miroslav Benes , Kees Cook , Al Viro , Arnd Bergmann , Dave Hansen , David Howells , Russell King , Andy Lutomirski , Will Drewry , Will Deacon , Catalin Marinas Cc: linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, x86-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, kernel-hardening-ZwoEplunGu1jrUoiu81ncdBPR1lH4CV8@public.gmane.org, Octavian Purdila List-Id: linux-api@vger.kernel.org On Wed, 2017-06-14 at 18:12 -0700, Thomas Garnier wrote: > Ensure the address limit is a user-mode segment before returning to > user-mode. Otherwise a process can corrupt kernel-mode memory and > elevate privileges [1]. > > The set_fs function sets the TIF_SETFS flag to force a slow path on > return. In the slow path, the address limit is checked to be USER_DS if > needed. > > The TIF_SETFS flag is added to _TIF_WORK_MASK shifting _TIF_SYSCALL_WORK > for arm instruction immediate support. The global work mask is too big > to used on a single instruction so adapt ret_fast_syscall. > > [1] https://bugs.chromium.org/p/project-zero/issues/detail?id=990 > > Signed-off-by: Thomas Garnier > --- > v10 redesigns the change to use work flags on set_fs as recommended by > Linus and agreed by others. > > Based on next-20170609 > --- >  arch/arm/include/asm/thread_info.h | 15 +++++++++------ >  arch/arm/include/asm/uaccess.h     |  2 ++ >  arch/arm/kernel/entry-common.S     |  9 +++++++-- >  arch/arm/kernel/signal.c           |  5 +++++ >  4 files changed, 23 insertions(+), 8 deletions(-) > > diff --git a/arch/arm/include/asm/thread_info.h b/arch/arm/include/asm/thread_info.h > index 776757d1604a..1d468b527b7b 100644 > --- a/arch/arm/include/asm/thread_info.h > +++ b/arch/arm/include/asm/thread_info.h > @@ -139,10 +139,11 @@ extern int vfp_restore_user_hwstate(struct user_vfp __user *, >  #define TIF_NEED_RESCHED 1 /* rescheduling necessary */ >  #define TIF_NOTIFY_RESUME 2 /* callback before returning to user */ >  #define TIF_UPROBE 3 /* breakpointed or singlestepping */ > -#define TIF_SYSCALL_TRACE 4 /* syscall trace active */ > -#define TIF_SYSCALL_AUDIT 5 /* syscall auditing active */ > -#define TIF_SYSCALL_TRACEPOINT 6 /* syscall tracepoint instrumentation */ > -#define TIF_SECCOMP 7 /* seccomp syscall filtering active */ > +#define TIF_FSCHECK 4 /* Check FS is USER_DS on return */ > +#define TIF_SYSCALL_TRACE 5 /* syscall trace active */ > +#define TIF_SYSCALL_AUDIT 6 /* syscall auditing active */ > +#define TIF_SYSCALL_TRACEPOINT 7 /* syscall tracepoint instrumentation */ > +#define TIF_SECCOMP 8 /* seccomp syscall filtering active */ >   >  #define TIF_NOHZ 12 /* in adaptive nohz mode */ >  #define TIF_USING_IWMMXT 17 > @@ -153,6 +154,7 @@ extern int vfp_restore_user_hwstate(struct user_vfp __user *, >  #define _TIF_NEED_RESCHED (1 << TIF_NEED_RESCHED) >  #define _TIF_NOTIFY_RESUME (1 << TIF_NOTIFY_RESUME) >  #define _TIF_UPROBE (1 << TIF_UPROBE) > +#define _TIF_FSCHECK (1 << TIF_FSCHECK) >  #define _TIF_SYSCALL_TRACE (1 << TIF_SYSCALL_TRACE) >  #define _TIF_SYSCALL_AUDIT (1 << TIF_SYSCALL_AUDIT) >  #define _TIF_SYSCALL_TRACEPOINT (1 << TIF_SYSCALL_TRACEPOINT) > @@ -166,8 +168,9 @@ extern int vfp_restore_user_hwstate(struct user_vfp __user *, >  /* >   * Change these and you break ASM code in entry-common.S >   */ > -#define _TIF_WORK_MASK (_TIF_NEED_RESCHED | _TIF_SIGPENDING | \ > -  _TIF_NOTIFY_RESUME | _TIF_UPROBE) > +#define _TIF_WORK_MASK (_TIF_NEED_RESCHED | _TIF_SIGPENDING | \ > +  _TIF_NOTIFY_RESUME | _TIF_UPROBE | \ > +  _TIF_FSCHECK) >   >  #endif /* __KERNEL__ */ >  #endif /* __ASM_ARM_THREAD_INFO_H */ > diff --git a/arch/arm/include/asm/uaccess.h b/arch/arm/include/asm/uaccess.h > index 2577405d082d..6cc882223e34 100644 > --- a/arch/arm/include/asm/uaccess.h > +++ b/arch/arm/include/asm/uaccess.h > @@ -77,6 +77,8 @@ static inline void set_fs(mm_segment_t fs) >  { >   current_thread_info()->addr_limit = fs; >   modify_domain(DOMAIN_KERNEL, fs ? DOMAIN_CLIENT : DOMAIN_MANAGER); > + /* On user-mode return, check fs is correct */ > + set_thread_flag(TIF_FSCHECK); >  } >   >  #define segment_eq(a, b) ((a) == (b)) > diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S > index eb5cd77bf1d8..e33c32d56193 100644 > --- a/arch/arm/kernel/entry-common.S > +++ b/arch/arm/kernel/entry-common.S > @@ -41,7 +41,9 @@ ret_fast_syscall: >   UNWIND(.cantunwind ) >   disable_irq_notrace @ disable interrupts >   ldr r1, [tsk, #TI_FLAGS] @ re-check for syscall tracing > - tst r1, #_TIF_SYSCALL_WORK | _TIF_WORK_MASK > + tst r1, #_TIF_SYSCALL_WORK > + bne fast_work_pending > + tst r1, #_TIF_WORK_MASK >   bne fast_work_pending >   >   /* perform architecture specific actions before user return */ > @@ -67,12 +69,15 @@ ret_fast_syscall: >   str r0, [sp, #S_R0 + S_OFF]! @ save returned r0 >   disable_irq_notrace @ disable interrupts >   ldr r1, [tsk, #TI_FLAGS] @ re-check for syscall tracing > - tst r1, #_TIF_SYSCALL_WORK | _TIF_WORK_MASK > + tst r1, #_TIF_SYSCALL_WORK > + bne fast_work_pending > + tst r1, #_TIF_WORK_MASK >   beq no_work_pending >   UNWIND(.fnend ) >  ENDPROC(ret_fast_syscall) >   >   /* Slower path - fall through to work_pending */ > +fast_work_pending: >  #endif >   >   tst r1, #_TIF_SYSCALL_WORK > diff --git a/arch/arm/kernel/signal.c b/arch/arm/kernel/signal.c > index 7b8f2141427b..3a48b54c6405 100644 > --- a/arch/arm/kernel/signal.c > +++ b/arch/arm/kernel/signal.c > @@ -14,6 +14,7 @@ >  #include >  #include >  #include > +#include >   >  #include >  #include > @@ -571,6 +572,10 @@ do_work_pending(struct pt_regs *regs, unsigned int thread_flags, int syscall) >    * Update the trace code with the current status. >    */ >   trace_hardirqs_off(); > + > + /* Check valid user FS if needed */ > + addr_limit_user_check(); > + >   do { >   if (likely(thread_flags & _TIF_NEED_RESCHED)) { >   schedule(); This patch made it's way into linux-next next-20170717 and it seems to cause hangs when booting some boards over NFS (found via bisection). I don't know exactly what determines the issue but I can reproduce hangs if even if I just boot with init=/bin/bash and do stuff like # sleep 1 & sleep 1 & sleep 1 & wait; wait; wait; echo done! When this happens sysrq-t shows a sleep task hung in the 'R' state spinning in do_work_pending, so maybe there is a potential infinite loop here? The addr_limit_user_check at the start of do_work_pending will check for TIF_FSCHECK once and clear it but the function loops while (thread_flags & _TIF_WORK_MASK), so it if TIF_FSCHECK is set again then the loop will never terminate. Does this make sense? I added some instrumentation to check if TIF_FSCHECK can show up during the do_work_pending loop and the answer seems to be yes. I also tried to get a stack with a set_fs call from inside do_work_pending and got the following: [  227.582402] CPU: 0 PID: 829 Comm: sleep Not tainted 4.12.0-01057-g93af8f7-dirty #332 [  227.590171] Hardware name: Freescale i.MX6 SoloLite (Device Tree) [  227.596275] Backtrace:  [  227.598754] [] (dump_backtrace) from [] (show_stack+0x18/0x1c) [  227.606339]  r7:00000000 r6:60070113 r5:00000000 r4:c105a958 [  227.612016] [] (show_stack) from [] (dump_stack+0xb4/0xe8) [  227.619258] [] (dump_stack) from [] (mydbg_set_fs+0x40/0x48) [  227.626671]  r9:c08cf35c r8:ee1cda7c r7:ee1e3dce r6:bf000000 r5:00000000 r4:ffffe000 [  227.634433] [] (mydbg_set_fs) from [] (__probe_kernel_read+0x44/0xd0) [  227.642629] [] (__probe_kernel_read) from [] (do_alignment+0x8c/0x75c) [  227.650909]  r10:ef085000 r9:c08cf35c r8:00000001 r7:ee1e3dce r6:c011b84c r5:ee1cdbe0 [  227.658748]  r4:00000000 r3:00000000 [  227.662338] [] (do_alignment) from [] (do_DataAbort+0x40/0xc0) [  227.669921]  r10:ef085000 r9:ee1cc000 r8:ee1cdbe0 r7:ee1e3dce r6:c011b84c r5:00000001 [  227.677760]  r4:c100dd3c [  227.680308] [] (do_DataAbort) from [] (__dabt_svc+0x64/0xa0) [  227.687714] Exception stack(0xee1cdbe0 to 0xee1cdc28) [  227.692780] dbe0: 9064a8c0 ee1e3de2 d82727d8 00000000 ee1b20c0 ee1e3dce 00000000 ef08572c [  227.700971] dc00: c0bb2034 c10c75ea ef085000 ee1cdc74 ee1cdc00 ee1cdc30 c01761a8 c08cf35c [  227.709158] dc20: 40070113 ffffffff [  227.712661]  r8:c0bb2034 r7:ee1cdc14 r6:ffffffff r5:40070113 r4:c08cf35c [  227.719382] [] (inet_gro_receive) from [] (dev_gro_receive+0x2f0/0x618) [  227.727746]  r10:ef085000 r9:00000001 r8:00000000 r7:ef085710 r6:c1008b88 r5:ee1b20c0 [  227.735585]  r4:c1009f78 [  227.738132] [] (dev_gro_receive) from [] (napi_gro_receive+0x78/0x1f4) [  227.746410]  r10:ef085000 r9:00000001 r8:c10d15ec r7:c100792c r6:ef085710 r5:c10c744e [  227.754249]  r4:ee1b20c0 [  227.756801] [] (napi_gro_receive) from [] (fec_enet_rx_napi+0x39c/0x988) [  227.765253]  r9:00000001 r8:f0c8a960 r7:00000000 r6:00000000 r5:ef086000 r4:ee1b20c0 [  227.773010] [] (fec_enet_rx_napi) from [] (net_rx_action+0x21c/0x474) [  227.781201]  r10:ee1cdd78 r9:c0fa7b80 r8:ef7dab80 r7:0000012c r6:00000040 r5:00000001 [  227.789039]  r4:ef085710 [  227.791593] [] (net_rx_action) from [] (__do_softirq+0x158/0x534) [  227.799437]  r10:00000008 r9:ee1cc000 r8:c10ce568 r7:c100792c r6:c10247bd r5:00000003 [  227.807275]  r4:c100208c [  227.809824] [] (__do_softirq) from [] (irq_exit+0xec/0x168) [  227.817147]  r10:c1007ea0 r9:ef010400 r8:00000001 r7:00000000 r6:c1007d3c r5:00000000 [  227.824984]  r4:c0fa534c [  227.827534] [] (irq_exit) from [] (__handle_domain_irq+0x74/0xe8) [  227.835377] [] (__handle_domain_irq) from [] (gic_handle_irq+0x58/0xbc) [  227.843742]  r9:f080b100 r8:c105ae80 r7:ee1cde80 r6:000003ff r5:000003eb r4:f080b10c [  227.851498] [] (gic_handle_irq) from [] (__irq_svc+0x70/0x98) [  227.858990] Exception stack(0xee1cde80 to 0xee1cdec8) [  227.864056] de80: ee7a1140 00000001 00000000 000012a9 ee7a1140 ee9d9f10 ee76edc0 ee9d9f60 [  227.872248] dea0: 00000000 ee9d9f10 00000010 ee1cdeec ee1cdeb8 ee1cded0 c038a77c c0389688 [  227.880434] dec0: 60070013 ffffffff [  227.883937]  r10:00000010 r9:ee1cc000 r8:00000000 r7:ee1cdeb4 r6:ffffffff r5:60070013 [  227.891775]  r4:c0389688 [  227.894327] [] (nfs_file_clear_open_context) from [] (nfs_file_release+0x54/0x60) [  227.903558]  r7:ee9a78a0 r6:ee68f010 r5:ee9d9f10 r4:ee76edc0 [  227.909235] [] (nfs_file_release) from [] (__fput+0x94/0x1e0) [  227.916734] [] (__fput) from [] (____fput+0x10/0x14) [  227.923448]  r10:c10d4298 r9:00000000 r8:00000000 r7:ef2ed780 r6:ef2edc00 r5:c10d5180 [  227.931286]  r4:ef2edbd4 [  227.933839] [] (____fput) from [] (task_work_run+0xc8/0xec) [  227.941166] [] (task_work_run) from [] (do_work_pending+0x12c/0x1c4) [  227.949271]  r9:ee1cdfb0 r8:00000000 r7:00000000 r6:ee1cc000 r5:00000000 r4:00000000 [  227.957029] [] (do_work_pending) from [] (slow_work_pending+0xc/0x20) [  227.965219]  r10:00000000 r9:ee1cc000 r8:c0107e24 r7:0000005b r6:b6f76568 r5:b6f741f0 [  227.973058]  r4:b6f76904 Maybe the reason this reproduces easily in this particular setup is that ethernet causes lots of alignment faults? -- Regards, Leonard