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Subject: Re: [PATCH] powerpc: don't select KFENCE on platform PPC_FSL_BOOK3E
To:     Marco Elver <elver@google.com>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>
References: <20210924063927.1341241-1-liushixin2@huawei.com>
CC:     <linuxppc-dev@lists.ozlabs.org>, <linux-kernel@vger.kernel.org>
From:   Liu Shixin <liushixin2@huawei.com>
Message-ID: <77ce95e4-1af1-6536-5f0c-a573c648801a@huawei.com>
Date:   Tue, 12 Oct 2021 09:43:21 +0800
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kindly ping.


On 2021/9/24 14:39, Liu Shixin wrote:
> On platform PPC_FSL_BOOK3E, all lowmem is managed by tlbcam. That means
> we didn't really map the kfence pool with page granularity. Therefore,
> if KFENCE is enabled, the system will hit the following panic:
>
>     BUG: Kernel NULL pointer dereference on read at 0x00000000
>     Faulting instruction address: 0xc01de598
>     Oops: Kernel access of bad area, sig: 11 [#1]
>     BE PAGE_SIZE=4K SMP NR_CPUS=4 MPC8544 DS
>     Dumping ftrace buffer:
>        (ftrace buffer empty)
>     Modules linked in:
>     CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.12.0-rc3+ #298
>     NIP:  c01de598 LR: c08ae9c4 CTR: 00000000
>     REGS: c0b4bea0 TRAP: 0300   Not tainted  (5.12.0-rc3+)
>     MSR:  00021000 <CE,ME>  CR: 24000228  XER: 20000000
>     DEAR: 00000000 ESR: 00000000
>     GPR00: c08ae9c4 c0b4bf60 c0ad64e0 ef720000 00021000 00000000 00000000 00000200
>     GPR08: c0ad5000 00000000 00000000 00000004 00000000 008fbb30 00000000 00000000
>     GPR16: 00000000 00000000 00000000 00000000 c0000000 00000000 00000000 00000000
>     GPR24: c08ca004 c08ca004 c0b6a0e0 c0b60000 c0b58f00 c0850000 c08ca000 ef720000
>     NIP [c01de598] kfence_protect+0x44/0x6c
>     LR [c08ae9c4] kfence_init+0xfc/0x2a4
>     Call Trace:
>     [c0b4bf60] [efffe160] 0xefffe160 (unreliable)
>     [c0b4bf70] [c08ae9c4] kfence_init+0xfc/0x2a4
>     [c0b4bfb0] [c0894d3c] start_kernel+0x3bc/0x574
>     [c0b4bff0] [c0000470] set_ivor+0x14c/0x188
>     Instruction dump:
>     7c0802a6 8109d594 546a653a 90010014 54630026 39200000 7d48502e 2c0a0000
>     41820010 554a0026 5469b53a 7d295214 <81490000> 38831000 554a003c 91490000
>     random: get_random_bytes called from print_oops_end_marker+0x40/0x78 with crng_init=0
>     ---[ end trace 0000000000000000 ]---
>
> Signed-off-by: Liu Shixin <liushixin2@huawei.com>
> ---
>  arch/powerpc/Kconfig | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index d46db0bfb998..cffd57bcb5e4 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -185,7 +185,7 @@ config PPC
>  	select HAVE_ARCH_KASAN			if PPC32 && PPC_PAGE_SHIFT <= 14
>  	select HAVE_ARCH_KASAN_VMALLOC		if PPC32 && PPC_PAGE_SHIFT <= 14
>  	select HAVE_ARCH_KGDB
> -	select HAVE_ARCH_KFENCE			if PPC32
> +	select HAVE_ARCH_KFENCE			if PPC32 && !PPC_FSL_BOOK3E
>  	select HAVE_ARCH_MMAP_RND_BITS
>  	select HAVE_ARCH_MMAP_RND_COMPAT_BITS	if COMPAT
>  	select HAVE_ARCH_NVRAM_OPS