On Tue, 10 Jul 2018, Greg Kroah-Hartman wrote:
[Adding the stable list] On Mon, Jul 09, 2018 at 11:53:37PM -0700, Victor Kamensky wrote:Hi Masami, I am not sure maybe you are aware about this issue already, but I am writing in case if you are not. After move to 4.4.131 stable very basic SystemTap script that involves kprobes stopped working - it crashes kernel. The SystemTap script like this: probe kernel.function("meminfo_proc_show") { println("meminfo_proc_show called") } which effectively will translate into kprobe entry in meminfo_proc_show function, crashes like this. BUG: unable to handle kernel paging request at ffffffffc063f002 IP: [<ffffffffa3c3558b>] resume_execution+0xe5/0x151 PGD 24613067 ca PUD 24615067 PMD 1523e9067 PTE 3370d061 Oops: 0003 [#1] SMP Modules linked in: <snip> CPU: 3 PID: 20078 Comm: <snip> Tainted: G O 4.4.131 #1 task: ffff880031ead780 ti: ffff880032238000 task.ti: ffff880032238000 t /RIP: 0010:[<ffffffffa3c3558b>] [<ffffffffa3c3558b>] resume_execution+0xe5/0x151 RSP: 0018:ffff88017fccaec8 EFLAGS: 00010006 RAX: ffffffffa3dad154 RBX: ffffffffa3dad152 RCX: 000000003f9c0ff9 RDX: ffffffffc063f002 RSI: ffff88017fccaf58 RDI: 0000000000000041 RBP: ffff8801549f83c0 R08: 0000000000000001 R09: 0000000000000001 R10: ffff88003223bdd8 R11: 0000000000000246 R12: ffff88003223bdd8 R13: ffff88017fccaf58 R14: ffffffffc063f000 R15: ffff88017fccee40 FS: 00007f9f34520240(0000) GS:ffff88017fcc0000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: ffffffffc063f002 CR3: 0000000152b46000 CR4: 0000000000100670 Stack: ffff88017fccee40 ffff88017fccaf58 ffff8801549f83c0 0000000000000000 ffff880033cde500 0000000000000001 ffffffffa3c35633 ffff88017fccaf58 ffff880031ead780 0000000000000000 ffffffffa3c04e9d 0000000000004000 Call Trace: <#DB> [<ffffffffa3c35633>] ? kprobe_debug_handler+0x3c/0xc8 [<ffffffffa3c04e9d>] ? do_debug+0x7a/0x182 [<ffffffffa4163afe>] ? debug+0x3e/0x70 [<ffffffffa3dad14d>] ? meminfo_proc_open+0x1c/0x1c [<ffffffffa3d73111>] ? seq_buf_alloc+0x23/0x3c <<EOE>> [<ffffffffa3d735a8>] ? seq_read+0x1a6/0x40d [<ffffffffa3da5700>] ? proc_reg_read+0x47/0x65 [<ffffffffa3da56b9>] ? proc_reg_write+0x65/0x65 [<ffffffffa3d55ebf>] ? __vfs_read+0x34/0xea [<ffffffffa3d564f9>] ? rw_verify_area+0x7a/0xc9 [<ffffffffa3d565dc>] ? vfs_read+0x94/0xf9 [<ffffffffa3d570a4>] ? SyS_read+0x61/0xb4 [<ffffffffa4161b8a>] ? entry_SYSCALL_64_fastpath+0x1e/0x8e Code: 7d 70 00 75 3e 49 8b 95 80 00 00 00 49 39 d6 73 2b 48 89 d0 4c 29 f0 48 8d 48 05 48 83 f9 0e 77 1b b9 fb ff ff ff 48 01 d8 29 d1 <c6> 02 e9 01 c8 89 42 01 c7 45 70 01 00 00 00 eb 07 c7 45 70 ff RIP [<ffffffffa3c3558b>] resume_execution+0xe5/0x151 RSP <ffff88017fccaec8> CR2: ffffffffc063f002 Decoding crash: (gdb) p &resume_execution $1 = (void (*)(struct kprobe *, struct pt_regs *, struct kprobe_ctlblk *)) 0xffffffff810354a6 <resume_execution> (gdb) b *(0xffffffff810354a6 + 0xe5) Breakpoint 1 at 0xffffffff8103558b: file <snip>/kernel-source/arch/x86/kernel/kprobes/core.c, line 126. corresponds to: static nokprobe_inline void __synthesize_relative_insn(void *from, void *to, u8 op) { struct __arch_relative_insn { u8 op; s32 raddr; } __packed *insn; insn = (struct __arch_relative_insn *)from; insn->raddr = (s32)((long)(to) - ((long)(from) + 5)); insn->op = op; <---------------------------------------- } (gdb) p /x &kprobe_debug_handler $1 = 0xffffffff810355f7 (gdb) b *(0xffffffff810355f7 + 0x3c) Breakpoint 1 at 0xffffffff81035633: file <snip>/kernel-source/arch/x86/kernel/kprobes/core.c, line 932. corresponds to static void resume_execution(struct kprobe *p, struct pt_regs *regs, struct kprobe_ctlblk *kcb) { <snip> if (p->ainsn.boostable == 0) { if ((regs->ip > copy_ip) && (regs->ip - copy_ip) + 5 < MAX_INSN_SIZE) { /* * These instructions can be executed directly if it * jumps back to correct address. */ synthesize_reljump((void *)regs->ip, (void *)orig_ip + (regs->ip - copy_ip)); <------- p->ainsn.boostable = 1; } else { p->ainsn.boostable = -1; } } Further digging points to the following couple commits that 4.4.y stable picked up: 1dd26ec7 kprobes/x86: Fix to set RWX bits correctly before releasing trampoline 76bee4 kprobes/x86: Set kprobes pages read-only Effectively the way I read: the problem is that linux-4.4.y branch is missing your following commit commit 804dec5bda9b4fcdab5f67fe61db4a0498af5221 Author: Masami Hiramatsu <mhiramat@xxxxxxxxxx> Date: Wed Mar 29 14:00:25 2017 +0900 kprobes/x86: Do not modify singlestep buffer while resuming Do not modify singlestep execution buffer (kprobe.ainsn.insn) while resuming from single-stepping, instead, modifies the buffer to add a jump back instruction at preparing buffer. Signed-off-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx> Cc: Ananth N Mavinakayanahalli <ananth@xxxxxxxxxxxxxxxxxx> and as result synthesize_reljump function call still exists from resume_execution function but it does not have proper page permission manipulation code around it, so making kprobes pages as read-only has averse effect: I.e when called from resume_execution function it hits read-only page and crashes. Please advise how to proceed besides obvious backing out above mentioned two commits.So if you apply the above commit, all works properly for you?
That commit seems to be part of some x86 kprobes restructuring, I hesitated to try it. After your email tried to cherry-pick to 4.4.y and it does not go in smoothly at all, quite a bit of conflicts. I may not phrase it correctly: My point was that in 4.4 there are more places where synthesize_reljump function is called, which latter got removed. And this function modifies kprobes page, so lifting up read-only protection needs to be done in more places compared to latter kernels. Whether it can be done correctly and proper thing to do in do_debug/resume_execution function exception processing context I cannot tell. Thanks, Victor
thanks, greg k-h
