Subject: Re: 5.?? regression: strace testsuite OOpses kernel on ia64

From: Sergei Trofimovich <[email-masked]>
Date: Fri, 9 Apr 2021 22:20:04 +0100

On Tue, 23 Feb 2021 18:53:21 +0000
Sergei Trofimovich <[email-masked]> wrote:

> The crash seems to be related to sock_filter-v test from strace:
>     https://github.com/strace/strace/blob/master/tests/seccomp-filter-v.c
> 
> Here is an OOps:
> 
> [  818.089904] BUG: Bad page map in process sock_filter-v  pte:00000001 pmd:118580001
> [  818.089904] page:00000000e6a429c8 refcount:1 mapcount:-1 mapping:0000000000000000 index:0x0 pfn:0x0
> [  818.089904] flags: 0x1000(reserved)
> [  818.089904] raw: 0000000000001000 a000400000000008 a000400000000008 0000000000000000
> [  818.089904] raw: 0000000000000000 0000000000000000 00000001fffffffe
> [  818.089904] page dumped because: bad pte
> [  818.089904] addr:0000000000000000 vm_flags:04044011 anon_vma:0000000000000000 mapping:0000000000000000 index:0
> [  818.095483] file:(null) fault:0x0 mmap:0x0 readpage:0x0
> [  818.095483] CPU: 0 PID: 5990 Comm: sock_filter-v Not tainted 5.11.0-00003-gbfa5a4929c90 #57
> [  818.095483] Hardware name: hp server rx3600                   , BIOS 04.03                                                            04/08/2008
> [  818.095483]
> [  818.095483] Call Trace:
> [  818.095483]  [<a000000100014a70>] show_stack+0x90/0xc0
> [  818.095483]                                 sp=e000000118707bb0 bsp=e0000001187013c0
> [  818.095483]  [<a00000010100c2b0>] dump_stack+0x120/0x160
> [  818.095483]                                 sp=e000000118707d80 bsp=e000000118701348
> [  818.095483]  [<a0000001002e7b40>] print_bad_pte+0x300/0x3a0
> [  818.095483]                                 sp=e000000118707d80 bsp=e0000001187012e0
> [  818.099483]  [<a0000001002ec190>] unmap_page_range+0xa90/0x11a0
> [  818.099483]                                 sp=e000000118707d80 bsp=e000000118701140
> [  818.099483]  [<a0000001002ecba0>] unmap_vmas+0xc0/0x100
> [  818.099483]                                 sp=e000000118707da0 bsp=e000000118701108
> [  818.099483]  [<a000000100302db0>] exit_mmap+0x150/0x320
> [  818.099483]                                 sp=e000000118707da0 bsp=e0000001187010d8
> [  818.099483]  [<a00000010005dba0>] mmput+0x60/0x200
> [  818.099483]                                 sp=e000000118707e20 bsp=e0000001187010b0
> [  818.103482]  [<a00000010006e570>] do_exit+0x6f0/0x18a0
> [  818.103482]                                 sp=e000000118707e20 bsp=e000000118701038
> [  818.103482]  [<a000000100072070>] do_group_exit+0x90/0x2a0
> [  818.103482]                                 sp=e000000118707e30 bsp=e000000118700ff0
> [  818.103482]  [<a0000001000722a0>] sys_exit_group+0x20/0x40
> [  818.103482]                                 sp=e000000118707e30 bsp=e000000118700f98
> [  818.107482]  [<a00000010000c5f0>] ia64_trace_syscall+0xf0/0x130
> [  818.107482]                                 sp=e000000118707e30 bsp=e000000118700f98
> [  818.107482]  [<a000000000040720>] ia64_ivt+0xffffffff00040720/0x400
> [  818.107482]                                 sp=e000000118708000 bsp=e000000118700f98
> [  818.115482] Disabling lock debugging due to kernel taint
> [  818.115482] BUG: Bad rss-counter state mm:000000002eec6412 type:MM_FILEPAGES val:-1
> [  818.132256] Unable to handle kernel NULL pointer dereference (address 0000000000000068)
> [  818.133904] sock_filter-v-X[5999]: Oops 11012296146944 [1]
> [  818.133904] Modules linked in: acpi_ipmi ipmi_si usb_storage e1000 ipmi_devintf ipmi_msghandler rtc_efi
> [  818.133904]
> [  818.133904] CPU: 0 PID: 5999 Comm: sock_filter-v-X Tainted: G    B             5.11.0-00003-gbfa5a4929c90 #57
> [  818.133904] Hardware name: hp server rx3600                   , BIOS 04.03                                                            04/08/2008
> [  818.133904] psr : 0000121008026010 ifs : 8000000000000288 ip  : [<a0000001001eaa61>]    Tainted: G    B             (5.11.0-00003-gbfa5a4929c90)
> [  818.133904] ip is at bpf_prog_free+0x21/0xe0
> [  818.133904] unat: 0000000000000000 pfs : 0000000000000307 rsc : 0000000000000003
> [  818.133904] rnat: 0000000000000000 bsps: 0000000000000000 pr  : 00106a5a51665965
> [  818.133904] ldrs: 0000000000000000 ccv : 0000000012088904 fpsr: 0009804c8a70033f
> [  818.133904] csd : 0000000000000000 ssd : 0000000000000000
> [  818.133904] b0  : a000000100d54080 b6  : a000000100d53fe0 b7  : a00000010000cef0
> [  818.133904] f6  : 0ffefb0c50daa1b67f89a f7  : 0ffed8b3e4fdb08000000
> [  818.133904] f8  : 10017fbd1bc0000000000 f9  : 1000eb95f000000000000
> [  818.133904] f10 : 10008ade20716a6c83cc1 f11 : 1003e00000000000002b7
> [  818.133904] r1  : a00000010176b300 r2  : a000000200008004 r3  : 0000000000000000
> [  818.133904] r8  : 0000000000000008 r9  : e00000011873f800 r10 : e000000102c18600
> [  818.133904] r11 : e000000102c19600 r12 : e00000011873f7f0 r13 : e000000118738000
> [  818.133904] r14 : 0000000000000068 r15 : a000000200008028 r16 : e000000005606a70
> [  818.133904] r17 : e000000102c18600 r18 : e000000104370748 r19 : e000000102c18600
> [  818.133904] r20 : e000000102c18600 r21 : e000000005606a78 r22 : a00000010156bd28
> [  818.133904] r23 : a00000010147fdf4 r24 : 0000000000004000 r25 : e000000104370750
> [  818.133904] r26 : a0000001012f7088 r27 : a000000100d53fe0 r28 : 0000000000000001
> [  818.133904] r29 : e00000011873f800 r30 : e00000011873f810 r31 : e00000011873f808
> [  818.133904]
> [  818.133904] Call Trace:
> [  818.133904]  [<a000000100014a70>] show_stack+0x90/0xc0
> [  818.133904]                                 sp=e00000011873f420 bsp=e0000001187396d0
> [  818.133904]  [<a000000100015170>] show_regs+0x6d0/0xa40
> [  818.133904]                                 sp=e00000011873f5f0 bsp=e000000118739660
> [  818.133904]  [<a000000100026e90>] die+0x1b0/0x4a0
> [  818.133904]                                 sp=e00000011873f610 bsp=e000000118739620
> [  818.133904]  [<a000000100059220>] ia64_do_page_fault+0x820/0xb60
> [  818.133904]                                 sp=e00000011873f610 bsp=e000000118739580
> [  818.133904]  [<a00000010000c8e0>] ia64_leave_kernel+0x0/0x270
> [  818.133904]                                 sp=e00000011873f620 bsp=e000000118739580
> [  818.133904]  [<a0000001001eaa60>] bpf_prog_free+0x20/0xe0
> [  818.133904]                                 sp=e00000011873f7f0 bsp=e000000118739540
> [  818.133904]  [<a000000100d54080>] sk_filter_release_rcu+0xa0/0x120
> [  818.133904]                                 sp=e00000011873f7f0 bsp=e000000118739510
> [  818.133904]  [<a00000010016a7f0>] rcu_core+0x530/0xf20
> [  818.133904]                                 sp=e00000011873f7f0 bsp=e0000001187394a8
> [  818.133904]  [<a00000010016b200>] rcu_core_si+0x20/0x40
> [  818.133904]                                 sp=e00000011873f810 bsp=e000000118739490
> [  818.133904]  [<a0000001010279f0>] __do_softirq+0x230/0x640
> [  818.133904]                                 sp=e00000011873f810 bsp=e0000001187393a0
> [  818.133904]  [<a000000100074770>] irq_exit+0x170/0x200
> [  818.133904]                                 sp=e00000011873f810 bsp=e000000118739388
> [  818.133904]  [<a000000100013310>] ia64_handle_irq+0x1b0/0x360
> [  818.133904]                                 sp=e00000011873f810 bsp=e000000118739308
> [  818.133904]  [<a00000010000c8e0>] ia64_leave_kernel+0x0/0x270
> [  818.133904]                                 sp=e00000011873f820 bsp=e000000118739308
> [  818.133904]  [<a000000101027700>] flush_icache_range+0x80/0xa0
> [  818.133904]                                 sp=e00000011873f9f0 bsp=e0000001187392f8
> [  818.133904]  [<a0000001002f7ae0>] __access_remote_vm+0x1e0/0x320
> [  818.133904]                                 sp=e00000011873f9f0 bsp=e000000118739258
> [  818.133904]  [<a0000001002f7c80>] access_process_vm+0x60/0xa0
> [  818.133904]                                 sp=e00000011873fa00 bsp=e000000118739210
> [  818.133904]  [<a000000100018210>] ia64_sync_user_rbs+0x70/0xe0
> [  818.133904]                                 sp=e00000011873fa00 bsp=e0000001187391d0
> [  818.133904]  [<a000000100018b00>] do_sync_rbs+0xc0/0x100
> [  818.133904]                                 sp=e00000011873fa10 bsp=e000000118739198
> [  818.133904]  [<a00000010000cf30>] unw_init_running+0x70/0xa0
> [  818.133904]                                 sp=e00000011873fa10 bsp=e000000118739170
> [  818.133904]  [<a00000010001ae90>] ia64_ptrace_stop+0x130/0x160
> [  818.133904]                                 sp=e00000011873fdf0 bsp=e000000118739158
> [  818.133904]  [<a00000010008af60>] ptrace_stop+0xc0/0x880
> [  818.133904]                                 sp=e00000011873fdf0 bsp=e000000118739118
> [  818.133904]  [<a00000010008b820>] ptrace_do_notify+0x100/0x120
> [  818.133904]                                 sp=e00000011873fdf0 bsp=e0000001187390e8
> [  818.133904]  [<a00000010008b8d0>] ptrace_notify+0x90/0x260
> [  818.133904]                                 sp=e00000011873fe30 bsp=e0000001187390c8
> [  818.133904]  [<a00000010001e3d0>] syscall_trace_enter+0xf0/0x2c0
> [  818.133904]                                 sp=e00000011873fe30 bsp=e000000118739070
> [  818.133904]  [<a00000010000c540>] ia64_trace_syscall+0x40/0x130
> [  818.133904]                                 sp=e00000011873fe30 bsp=e000000118739020
> [  818.186114] Kernel panic - not syncing: Aiee, killing interrupt handler!
> [  818.186114] ---[ end Kernel panic - not syncing: Aiee, killing interrupt handler! ]---
> 
> I'm not sure how to interpret it. It looks like 'bpf_prog_free'
> frees the memory that is not there anymore, but previous crash
> hints at already broken page tables. Maybe VM is already corrupted
> by previous strace tests?
> 
> I wonder if I can enable a bit more kernel VM debugging to catch the corruption earlier.

I threw a bunch of CONFIG_DEBUG_* options at the kernel.
None of them exposed any extra details or changed initial crash report.

I found out a few workarounds:

Workaround 1: switching vmalloc() to kmalloc() in kernel/bpf/core.c makes
the crash disappear (largeish patch: https://bugs.gentoo.org/769614#c26).
That might hint at the bug in ia64's virtual memory implementation
(like missing tlb flush?) but nothing else seems to exhibit any problems.

Workaround 2: switching sk_filter_release() from RCU free to inline free:

--- a/net/core/filter.c
+++ b/net/core/filter.c
 static void sk_filter_release(struct sk_filter *fp)
 {
 	if (refcount_dec_and_test(&fp->refcnt))
-		call_rcu(&fp->rcu, sk_filter_release_rcu);
+		//call_rcu(&fp->rcu, sk_filter_release_rcu);
+		__sk_filter_release(fp);
 }

+netdev@, +bpf@ for possible debugging help.

Now I can easily trigger the failure with the following test program:

$ cat bug.c
#include <unistd.h>
#include <netinet/in.h>
#include <sys/socket.h>
#include <linux/filter.h>

int
main(void)
{
	struct sock_filter bpf_filter[] = {
		BPF_STMT(BPF_RET|BPF_K, 0)
	};
	struct sock_fprog prog = {
		.len = 1,
		.filter = bpf_filter,
	};

	int fd = socket(AF_INET, SOCK_DGRAM, 0);
	setsockopt(fd, SOL_SOCKET, SO_ATTACH_FILTER, &prog, sizeof(prog));

	return 0;
}

$ gcc bug.c -o bug; while ./bug; do echo again; done

After 8 iterations machine crashes.

If I interpret backtrace correctly:

> [  818.133904]  [<a0000001001eaa60>] bpf_prog_free+0x20/0xe0
> [  818.133904]                                 sp=e00000011873f7f0 bsp=e000000118739540

; void bpf_prog_free(struct bpf_prog *fp):
; fp is in r32
Dump of assembler code for function bpf_prog_free:
   0xa00000010023bea0 <+0>:	[MMI]       alloc r35=ar.pfs,8,5,0
   0xa00000010023bea1 <+1>:	            adds r32=56,r32               ; r32 = fp + 56 (&fp->aux)
   0xa00000010023bea2 <+2>:	            mov r34=b0;;
   0xa00000010023beb0 <+16>:	[MMI]       ld8 r33=[r32];;             ; r33 = fp->aux
   0xa00000010023beb1 <+17>:	            adds r14=112,r33              ; r14 = &(fp->aux->dst_prog)
   0xa00000010023beb2 <+18>:	            nop.i 0x0;;
   0xa00000010023bec0 <+32>:	[MMI]       nop.m 0x0
   0xa00000010023bec1 <+33>:	            ld8 r37=[r14]                   ; r37 = fp->aux->dst_prog
   0xa00000010023bec2 <+34>:	            nop.i 0x0;;

kernel crashes on aux NULL-ish dereference of fp->aux->dst_prog at:

> [  818.133904] r14 : 0000000000000068 r15 : a000000200008028 r16 : e000000005606a70

/* Free internal BPF program */
void bpf_prog_free(struct bpf_prog *fp)
{
        struct bpf_prog_aux *aux = fp->aux;

        if (aux->dst_prog)
                bpf_prog_put(aux->dst_prog);
        INIT_WORK(&aux->work, bpf_prog_free_deferred);
        schedule_work(&aux->work);
}

Could it be that fp->aux is sometimes free'd earlier than it should?
It's a non-preemptible kernel.

-- 

  Sergei