Messages in this thread | | | Date | Fri, 1 May 2020 00:17:06 -0500 | From | Josh Poimboeuf <> | Subject | Re: [RFC][PATCH] x86/ftrace: Have ftrace trampolines turn read-only at the end of system boot up |
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On Thu, Apr 30, 2020 at 11:47:33PM -0500, Josh Poimboeuf wrote: > On Thu, Apr 30, 2020 at 08:21:47PM -0400, Steven Rostedt wrote: > > The cause is the "ftrace=function" would register the function tracer > > and create a trampoline, and it will set it as executable and > > read-only. Then the "trace_options=func_stack_trace" would then update > > the same trampoline to include the stack tracer version of the function > > tracer. But since the trampoline already exists, it updates it with > > text_poke_bp(). The problem is that text_poke_bp() called while > > system_state == SYSTEM_BOOTING, it will simply do a memcpy() and not > > the page mapping, as it would think that the text is still read-write. > > But in this case it is not, and we take a fault and crash. > > > > Instead, lets keep the ftrace trampolines read-write during boot up, > > and then when the kernel executable text is set to read-only, the > > ftrace trampolines get set to read-only as well. > > Would it be easier to just call a new __text_poke_bp() which skips the > SYSTEM_BOOTING check, since you know the trampoline will always be > read-only? > > Like:
early_trace_init() is called after mm_init(), so I thought it might work, but I guess not:
[ 0.206271] Starting tracer 'function' [ 0.232032] BUG: kernel NULL pointer dereference, address: 0000000000000050 [ 0.232035] #PF: supervisor read access in kernel mode [ 0.232036] #PF: error_code(0x0000) - not-present page [ 0.232037] PGD 0 P4D 0 [ 0.232040] Oops: 0000 [#1] PREEMPT SMP PTI [ 0.232042] CPU: 0 PID: 0 Comm: swapper Not tainted 5.7.0-rc2-next-20200424+ #127 [ 0.232043] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-2.fc30 04/01/2014 [ 0.232047] RIP: 0010:walk_to_pmd+0x11/0x140 [ 0.232048] Code: 78 c1 32 82 e8 a0 68 ff ff 0f 0b 66 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 0f 1f 44 00 00 48 89 f0 48 c1 e8 24 25 f8 0f 00 00 <48> 03 47 50 0f 84 12 01 00 00 41 54 49 89 fc 55 48 89 c5 53 48 8b [ 0.232050] RSP: 0000:ffffffff82603c68 EFLAGS: 00010046 [ 0.232051] RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000 [ 0.232052] RDX: ffffffff82603cc8 RSI: 0000000000000000 RDI: 0000000000000000 [ 0.232053] RBP: 8000000000000063 R08: 0000000000000001 R09: fff0000000000fff [ 0.232054] R10: 0000000000000000 R11: 0000000000000000 R12: ffffffff82603cc8 [ 0.232055] R13: 0000000000000000 R14: 0000000000000066 R15: fffffffffffffeff [ 0.232056] FS: 0000000000000000(0000) GS:ffff88813b600000(0000) knlGS:0000000000000000 [ 0.232057] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 0.232058] CR2: 0000000000000050 CR3: 0000000002612001 CR4: 00000000000606b0 [ 0.232061] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [ 0.232062] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 [ 0.232063] Call Trace: [ 0.232066] __get_locked_pte+0x19/0x100 [ 0.232069] ? 0xffffffffa0000065 [ 0.232071] __text_poke+0x14d/0x640 [ 0.232073] ? 0xffffffffa0000065 [ 0.232076] text_poke_bp_batch+0x8b/0x1c0 [ 0.232078] ? 0xffffffffa0000065 [ 0.232080] __text_poke_bp+0x3a/0x60 [ 0.232083] arch_ftrace_update_trampoline+0xac/0x300 [ 0.232087] __register_ftrace_function+0x7c/0xc0 [ 0.232089] ftrace_startup+0x1e/0xf0 [ 0.232091] register_ftrace_function+0x24/0x70 [ 0.232093] func_set_flag+0x6f/0x90 [ 0.232096] __set_tracer_option.isra.0+0x24/0x50 [ 0.232098] trace_set_options+0x149/0x160 [ 0.232102] apply_trace_boot_options+0x44/0x6d [ 0.232105] register_tracer+0x1d8/0x1e9 [ 0.232107] early_trace_init+0x266/0x378 [ 0.232109] start_kernel+0x337/0x614 [ 0.232112] ? x86_family+0x5/0x20 [ 0.232114] secondary_startup_64+0xa4/0xb0 [ 0.232119] Modules linked in: [ 0.232120] CR2: 0000000000000050 [ 0.232126] random: get_random_bytes called from print_oops_end_marker+0x26/0x40 with crng_init=0 [ 0.232128] ---[ end trace 71e23a89b9b5224f ]--- [ 0.232130] RIP: 0010:walk_to_pmd+0x11/0x140 [ 0.232131] Code: 78 c1 32 82 e8 a0 68 ff ff 0f 0b 66 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 0f 1f 44 00 00 48 89 f0 48 c1 e8 24 25 f8 0f 00 00 <48> 03 47 50 0f 84 12 01 00 00 41 54 49 89 fc 55 48 89 c5 53 48 8b [ 0.232133] RSP: 0000:ffffffff82603c68 EFLAGS: 00010046 [ 0.232134] RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000 [ 0.232135] RDX: ffffffff82603cc8 RSI: 0000000000000000 RDI: 0000000000000000 [ 0.232136] RBP: 8000000000000063 R08: 0000000000000001 R09: fff0000000000fff [ 0.232137] R10: 0000000000000000 R11: 0000000000000000 R12: ffffffff82603cc8 [ 0.232138] R13: 0000000000000000 R14: 0000000000000066 R15: fffffffffffffeff [ 0.232139] FS: 0000000000000000(0000) GS:ffff88813b600000(0000) knlGS:0000000000000000 [ 0.232140] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 0.232141] CR2: 0000000000000050 CR3: 0000000002612001 CR4: 00000000000606b0 [ 0.232142] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [ 0.232143] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 [ 0.232144] Kernel panic - not syncing: Attempted to kill the idle task! [ 0.232184] ---[ end Kernel panic - not syncing: Attempted to kill the idle task! ]---
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