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Message-ID: <94dbb4c5-e895-0909-d231-893812cc9bc0@linux.ibm.com>
Date:   Thu, 10 Nov 2022 16:08:56 +0100
MIME-Version: 1.0
Subject: Re: [PATCH v2] gcov: clang: fix the buffer overflow issue
To:     Mukesh Ojha <quic_mojha@quicinc.com>,
        Andrew Morton <akpm@linux-foundation.org>
Cc:     linux-kernel@vger.kernel.org, llvm@lists.linux.dev,
        nathan@kernel.org, ndesaulniers@google.com, trix@redhat.com
References: <1668020497-13142-1-git-send-email-quic_mojha@quicinc.com>
Content-Language: en-US
From:   Peter Oberparleiter <oberpar@linux.ibm.com>
In-Reply-To: <1668020497-13142-1-git-send-email-quic_mojha@quicinc.com>
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On 09.11.2022 20:01, Mukesh Ojha wrote:
> Currently, in clang version of gcov code when module is getting removed
> gcov_info_add() incorrectly adds the sfn_ptr->counter to all the
> dst->functions and it result in the kernel panic in below crash report.
> Fix this by properly handling it.
> 
> [    8.899094][  T599] Unable to handle kernel write to read-only memory at virtual address ffffff80461cc000
> [    8.899100][  T599] Mem abort info:
> [    8.899102][  T599]   ESR = 0x9600004f
> [    8.899103][  T599]   EC = 0x25: DABT (current EL), IL = 32 bits
> [    8.899105][  T599]   SET = 0, FnV = 0
> [    8.899107][  T599]   EA = 0, S1PTW = 0
> [    8.899108][  T599]   FSC = 0x0f: level 3 permission fault
> [    8.899110][  T599] Data abort info:
> [    8.899111][  T599]   ISV = 0, ISS = 0x0000004f
> [    8.899113][  T599]   CM = 0, WnR = 1
> [    8.899114][  T599] swapper pgtable: 4k pages, 39-bit VAs, pgdp=00000000ab8de000
> [    8.899116][  T599] [ffffff80461cc000] pgd=18000009ffcde003, p4d=18000009ffcde003, pud=18000009ffcde003, pmd=18000009ffcad003, pte=00600000c61cc787
> [    8.899124][  T599] Internal error: Oops: 9600004f [#1] PREEMPT SMP
> [    8.899265][  T599] Skip md ftrace buffer dump for: 0x1609e0
> ....
> ..,
> [    8.899544][  T599] CPU: 7 PID: 599 Comm: modprobe Tainted: G S         OE     5.15.41-android13-8-g38e9b1af6bce #1
> [    8.899547][  T599] Hardware name: XXX (DT)
> [    8.899549][  T599] pstate: 82400005 (Nzcv daif +PAN -UAO +TCO -DIT -SSBS BTYPE=--)
> [    8.899551][  T599] pc : gcov_info_add+0x9c/0xb8
> [    8.899557][  T599] lr : gcov_event+0x28c/0x6b8
> [    8.899559][  T599] sp : ffffffc00e733b00
> [    8.899560][  T599] x29: ffffffc00e733b00 x28: ffffffc00e733d30 x27: ffffffe8dc297470
> [    8.899563][  T599] x26: ffffffe8dc297000 x25: ffffffe8dc297000 x24: ffffffe8dc297000
> [    8.899566][  T599] x23: ffffffe8dc0a6200 x22: ffffff880f68bf20 x21: 0000000000000000
> [    8.899569][  T599] x20: ffffff880f68bf00 x19: ffffff8801babc00 x18: ffffffc00d7f9058
> [    8.899572][  T599] x17: 0000000000088793 x16: ffffff80461cbe00 x15: 9100052952800785
> [    8.899575][  T599] x14: 0000000000000200 x13: 0000000000000041 x12: 9100052952800785
> [    8.899577][  T599] x11: ffffffe8dc297000 x10: ffffffe8dc297000 x9 : ffffff80461cbc80
> [    8.899580][  T599] x8 : ffffff8801babe80 x7 : ffffffe8dc2ec000 x6 : ffffffe8dc2ed000
> [    8.899583][  T599] x5 : 000000008020001f x4 : fffffffe2006eae0 x3 : 000000008020001f
> [    8.899586][  T599] x2 : ffffff8027c49200 x1 : ffffff8801babc20 x0 : ffffff80461cb3a0
> [    8.899589][  T599] Call trace:
> [    8.899590][  T599]  gcov_info_add+0x9c/0xb8
> [    8.899592][  T599]  gcov_module_notifier+0xbc/0x120
> [    8.899595][  T599]  blocking_notifier_call_chain+0xa0/0x11c
> [    8.899598][  T599]  do_init_module+0x2a8/0x33c
> [    8.899600][  T599]  load_module+0x23cc/0x261c
> [    8.899602][  T599]  __arm64_sys_finit_module+0x158/0x194
> [    8.899604][  T599]  invoke_syscall+0x94/0x2bc
> [    8.899607][  T599]  el0_svc_common+0x1d8/0x34c
> [    8.899609][  T599]  do_el0_svc+0x40/0x54
> [    8.899611][  T599]  el0_svc+0x94/0x2f0
> [    8.899613][  T599]  el0t_64_sync_handler+0x88/0xec
> [    8.899615][  T599]  el0t_64_sync+0x1b4/0x1b8
> [    8.899618][  T599] Code: f905f56c f86e69ec f86e6a0f 8b0c01ec (f82e6a0c)
> [    8.899620][  T599] ---[ end trace ed5218e9e5b6e2e6 ]---
> 
> Signed-off-by: Mukesh Ojha <quic_mojha@quicinc.com>

Looks good to me! Successfully tested on s390.

Fixes: e178a5beb369 ("gcov: clang support")
Reviewed-by: Peter Oberparleiter <oberpar@linux.ibm.com>
Tested-by: Peter Oberparleiter <oberpar@linux.ibm.com>

And I'm not sure if this is strictly needed, but we could also add:

Cc: <stable@vger.kernel.org> # 5.2+

@Andrew: could you pick this up via your tree?

> ---
> v1..v2:
>  - Addressed Peter O. comment.
> 
>  kernel/gcov/clang.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/kernel/gcov/clang.c b/kernel/gcov/clang.c
> index cbb0bed..7670a81 100644
> --- a/kernel/gcov/clang.c
> +++ b/kernel/gcov/clang.c
> @@ -280,6 +280,8 @@ void gcov_info_add(struct gcov_info *dst, struct gcov_info *src)
>  
>  		for (i = 0; i < sfn_ptr->num_counters; i++)
>  			dfn_ptr->counters[i] += sfn_ptr->counters[i];
> +
> +		sfn_ptr = list_next_entry(sfn_ptr, head);
>  	}
>  }
>  

-- 
Peter Oberparleiter
Linux on IBM Z Development - IBM Germany R&D