Re: [PATCH v5 04/12] fprobe: Use ftrace_regs in fprobe entry handler

Masami Hiramatsu
2023-09-25T12:15:22Z

Hi Jiri,

On Mon, 25 Sep 2023 12:41:59 +0200
Jiri Olsa <olsajiri@gmail.com> wrote:

> On Sun, Sep 24, 2023 at 10:36:36PM +0900, Masami Hiramatsu (Google) wrote:
> > From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> >
> > This allows fprobes to be available with CONFIG_DYNAMIC_FTRACE_WITH_ARGS
> > instead of CONFIG_DYNAMIC_FTRACE_WITH_REGS, then we can enable fprobe
> > on arm64.
> >
> > Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> > Acked-by: Florent Revest <revest@chromium.org>
>
> I was getting bpf selftests failures with this patchset and when
> bisecting I'm getting crash when running on top of this change

Thanks for bisecting!

>
> looks like it's missing some of the regs NULL checks added later?

yeah, if the RIP (arch_rethook_prepare+0x0/0x30) is correct,

void arch_rethook_prepare(struct rethook_node *rh, struct ftrace_regs *fregs, bool mcount)

RSI (the 2nd argument) is NULL. This means fregs == NULL and caused the crash.
I think ftrace_get_regs(fregs) for the entry handler may return NULL.

Ah,

@@ -182,7 +182,7 @@ static void fprobe_init(struct fprobe *fp)
fp->ops.func = fprobe_kprobe_handler;
else
fp->ops.func = fprobe_handler;
- fp->ops.flags |= FTRACE_OPS_FL_SAVE_REGS;
+ fp->ops.flags |= FTRACE_OPS_FL_SAVE_ARGS;
}

static int fprobe_init_rethook(struct fprobe *fp, int num)

This may cause the issue, it should keep REGS at this point (this must be done in
[9/12]). But after applying [9/12], it shouldn't be a problem...

Let me check it again.

Thank you!

>
> jirka
>
>
> ---
> [ 124.089449][ T677] BUG: kernel NULL pointer dereference, address: 0000000000000098
> [ 124.090102][ T677] #PF: supervisor read access in kernel mode
> [ 124.090568][ T677] #PF: error_code(0x0000) - not-present page
> [ 124.091039][ T677] PGD 158fd8067 P4D 158fd8067 PUD 10896a067 PMD 0
> [ 124.091482][ T677] Oops: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC NOPTI
> [ 124.091986][ T677] CPU: 1 PID: 677 Comm: test_progs Tainted: G OE 6.6.0-rc2+ #768 1c8a8990289f2615e36dadd01915b80e8da29bf5
> [ 124.092898][ T677] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-1.fc38 04/01/2014
> [ 124.093613][ T677] RIP: 0010:arch_rethook_prepare+0x0/0x30
> [ 124.094060][ T677] Code: 90 90 90 90 90 90 90 90 90 90 48 89 b7 a8 00 00 00 c3 cc cc cc cc 0f 1f 40 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 <48> 8b 86 98 00 00 00 48 8b 10 48 89 57 20 48 8b 96 98 00 00 00 48
> [ 124.096239][ T677] RSP: 0018:ffffc90003d3bc98 EFLAGS: 00010286
> [ 124.096708][ T677] RAX: 0000000000000000 RBX: ffff88815d9fbe50 RCX: ffff88815d9fbe40
> [ 124.097332][ T677] RDX: 0000000000000001 RSI: 0000000000000000 RDI: ffff88815d9fbe40
> [ 124.097946][ T677] RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000004
> [ 124.098554][ T677] R10: 0000000000000001 R11: 0000000000000000 R12: ffffffff81fbb7b0
> [ 124.099108][ T677] R13: ffffffff81fbd47b R14: fffffffffffffff7 R15: ffff88815d9fbe40
> [ 124.099720][ T677] FS: 00007f9c2063ed00(0000) GS:ffff88846d200000(0000) knlGS:0000000000000000
> [ 124.100403][ T677] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [ 124.100908][ T677] CR2: 0000000000000098 CR3: 0000000108e02002 CR4: 0000000000770ee0
> [ 124.101537][ T677] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> [ 124.102096][ T677] DR3: 0000000000000000 DR6: 00000000ffff4ff0 DR7: 0000000000000400
> [ 124.102689][ T677] PKRU: 55555554
> [ 124.102988][ T677] Call Trace:
> [ 124.103303][ T677] <TASK>
> [ 124.103580][ T677] ? __die+0x1f/0x70
> [ 124.103928][ T677] ? page_fault_oops+0x176/0x4d0
> [ 124.104348][ T677] ? __pte_offset_map_lock+0xa5/0x190
> [ 124.104818][ T677] ? do_user_addr_fault+0x73/0x870
> [ 124.105277][ T677] ? exc_page_fault+0x81/0x250
> [ 124.105709][ T677] ? asm_exc_page_fault+0x22/0x30
> [ 124.106171][ T677] ? bpf_prog_test_run_tracing+0x14b/0x2c0
> [ 124.106675][ T677] ? __pfx_bpf_fentry_test1+0x10/0x10
> [ 124.107135][ T677] ? __pfx_arch_rethook_prepare+0x10/0x10
> [ 124.107598][ T677] rethook_hook+0x10/0x30
> [ 124.107966][ T677] fprobe_handler+0x129/0x210
> [ 124.108351][ T677] ? __pfx_bpf_fentry_test1+0x10/0x10
> [ 124.108796][ T677] ? bpf_prog_test_run_tracing+0x14b/0x2c0
> [ 124.109276][ T677] arch_ftrace_ops_list_func+0xf2/0x200
> [ 124.109708][ T677] ftrace_call+0x5/0x44
> [ 124.110060][ T677] ? bpf_fentry_test1+0x5/0x10
> [ 124.110463][ T677] bpf_fentry_test1+0x5/0x10
> [ 124.110881][ T677] bpf_prog_test_run_tracing+0x14b/0x2c0
> [ 124.111337][ T677] __sys_bpf+0x305/0x2820
> [ 124.111705][ T677] __x64_sys_bpf+0x1a/0x30
> [ 124.112053][ T677] do_syscall_64+0x38/0x90
> [ 124.116245][ T677] entry_SYSCALL_64_after_hwframe+0x6e/0xd8
> [ 124.116688][ T677] RIP: 0033:0x7f9c20806b5d
> [ 124.117078][ T677] Code: c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 f3 0f 1e fa 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 7b 92 0c 00 f7 d8 64 89 01 48
> [ 124.118487][ T677] RSP: 002b:00007ffc615e5228 EFLAGS: 00000206 ORIG_RAX: 0000000000000141
> [ 124.119090][ T677] RAX: ffffffffffffffda RBX: 00007f9c20918000 RCX: 00007f9c20806b5d
> [ 124.119698][ T677] RDX: 0000000000000050 RSI: 00007ffc615e5260 RDI: 000000000000000a
> [ 124.120298][ T677] RBP: 00007ffc615e5240 R08: 0000000000000000 R09: 00007ffc615e5260
> [ 124.120893][ T677] R10: 0000000000000064 R11: 0000000000000206 R12: 0000000000000001
> [ 124.121486][ T677] R13: 0000000000000000 R14: 00007f9c2094d000 R15: 00000000011a8db0
> [ 124.122156][ T677] </TASK>
> [ 124.122421][ T677] Modules linked in: bpf_testmod(OE) intel_rapl_msr intel_rapl_common crct10dif_pclmul crc32_pclmul crc32c_intel ghash_clmulni_intel kvm_intel rapl iTCO_wdt iTCO_vendor_support i2c_i801 i2c_smbus lpc_ich drm loop drm_panel_orientation_quirks zram
> [ 124.125064][ T677] CR2: 0000000000000098
> [ 124.125431][ T677] ---[ end trace 0000000000000000 ]---
> [ 124.125861][ T677] RIP: 0010:arch_rethook_prepare+0x0/0x30
> [ 124.126316][ T677] Code: 90 90 90 90 90 90 90 90 90 90 48 89 b7 a8 00 00 00 c3 cc cc cc cc 0f 1f 40 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 <48> 8b 86 98 00 00 00 48 8b 10 48 89 57 20 48 8b 96 98 00 00 00 48
> [ 124.127761][ T677] RSP: 0018:ffffc90003d3bc98 EFLAGS: 00010286
> [ 124.128238][ T677] RAX: 0000000000000000 RBX: ffff88815d9fbe50 RCX: ffff88815d9fbe40
> [ 124.128856][ T677] RDX: 0000000000000001 RSI: 0000000000000000 RDI: ffff88815d9fbe40
> [ 124.129502][ T677] RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000004
> [ 124.130129][ T677] R10: 0000000000000001 R11: 0000000000000000 R12: ffffffff81fbb7b0
> [ 124.130767][ T677] R13: ffffffff81fbd47b R14: fffffffffffffff7 R15: ffff88815d9fbe40
> [ 124.131410][ T677] FS: 00007f9c2063ed00(0000) GS:ffff88846d200000(0000) knlGS:0000000000000000
> [ 124.132084][ T677] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [ 124.132600][ T677] CR2: 0000000000000098 CR3: 0000000108e02002 CR4: 0000000000770ee0
> [ 124.133128][ T677] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> [ 124.133698][ T677] DR3: 0000000000000000 DR6: 00000000ffff4ff0 DR7: 0000000000000400
> [ 124.134302][ T677] PKRU: 55555554
> [ 124.134584][ T677] note: test_progs[677] exited with irqs disabled
> [ 124.135192][ T677] note: test_progs[677] exited with preempt_count 2

--
Masami Hiramatsu (Google) <mhiramat@kernel.org>