netdev - Re: [PATCH] powerpc/bpf: fix write protecting JIT code

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Date:   Mon, 25 Oct 2021 11:45:23 +0530
From:   "Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>
To:     ast@...nel.org, christophe.leroy@...roup.eu, daniel@...earbox.net,
        Hari Bathini <hbathini@...ux.ibm.com>, jniethe5@...il.com,
        mpe@...erman.id.au
Cc:     andrii@...nel.org, bpf@...r.kernel.org, john.fastabend@...il.com,
        kafai@...com, kpsingh@...nel.org, linuxppc-dev@...ts.ozlabs.org,
        netdev@...r.kernel.org, paulus@...ba.org, songliubraving@...com,
        stable@...r.kernel.org, yhs@...com
Subject: Re: [PATCH] powerpc/bpf: fix write protecting JIT code

Hari Bathini wrote:
> Running program with bpf-to-bpf function calls results in data access
> exception (0x300) with the below call trace:
> 
>     [c000000000113f28] bpf_int_jit_compile+0x238/0x750 (unreliable)
>     [c00000000037d2f8] bpf_check+0x2008/0x2710
>     [c000000000360050] bpf_prog_load+0xb00/0x13a0
>     [c000000000361d94] __sys_bpf+0x6f4/0x27c0
>     [c000000000363f0c] sys_bpf+0x2c/0x40
>     [c000000000032434] system_call_exception+0x164/0x330
>     [c00000000000c1e8] system_call_vectored_common+0xe8/0x278
> 
> as bpf_int_jit_compile() tries writing to write protected JIT code
> location during the extra pass.
> 
> Fix it by holding off write protection of JIT code until the extra
> pass, where branch target addresses fixup happens.
> 
> Cc: stable@...r.kernel.org
> Fixes: 62e3d4210ac9 ("powerpc/bpf: Write protect JIT code")
> Signed-off-by: Hari Bathini <hbathini@...ux.ibm.com>
> ---
>  arch/powerpc/net/bpf_jit_comp.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Thanks for the fix!

Reviewed-by: Naveen N. Rao <naveen.n.rao@...ux.vnet.ibm.com>