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[86.27.177.88]) by smtp.gmail.com with ESMTPSA id f8-20020a05600c154800b00397402ae674sm2636506wmg.11.2022.07.20.05.23.25 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 20 Jul 2022 05:23:26 -0700 (PDT) Date: Wed, 20 Jul 2022 13:23:24 +0100 From: Lee Jones To: =?utf-8?B?aGFpYmluemhhbmco5byg5rW35paMKQ==?= Cc: Catalin Marinas , Will Deacon , Ard Biesheuvel , Martin Ma , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" , "hewenliang4@huawei.com" Subject: Re: [PATCH V2] arm64: fix oops in concurrently setting insn_emulation sysctls Message-ID: References: <9A004C03-250B-46C5-BF39-782D7551B00E@tencent.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <9A004C03-250B-46C5-BF39-782D7551B00E@tencent.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, 02 Jul 2022, haibinzhang(张海斌) wrote: > How to reproduce: > launch two shell executions: > #!/bin/bash > while [ 1 ]; > do > echo 1 > /proc/sys/abi/swp > done > > Oops info: > Unable to handle kernel NULL pointer dereference at virtual address 0000000000000010 > Internal error: Oops: 96000006 [#1] SMP > Call trace: > update_insn_emulation_mode+0xc0/0x148 > emulation_proc_handler+0x64/0xb8 > proc_sys_call_handler+0x9c/0xf8 > proc_sys_write+0x18/0x20 > __vfs_write+0x20/0x48 > vfs_write+0xe4/0x1d0 > ksys_write+0x70/0xf8 > __arm64_sys_write+0x20/0x28 > el0_svc_common.constprop.0+0x7c/0x1c0 > el0_svc_handler+0x2c/0xa0 > el0_svc+0x8/0x200 > > emulation_proc_handler changes table->data for proc_dointvec_minmax > and so it isn't allowed to reenter before restoring table->data, > which isn't right now. > To fix this issue, keep the table->data as &insn->current_mode and > use container_of() to retrieve the insn pointer. Another mutex is > used to protect against the current_mode update but not for retrieving > insn_emulation as table->data is no longer changing. Looks as though this lost its Fixes tag during the rework. Fixes: 587064b610c7 ("arm64: Add framework for legacy instruction emulation") Will, are you able to add this retroactively? > Signed-off-by: hewenliang > Signed-off-by: Haibin Zhang > --- > arch/arm64/kernel/armv8_deprecated.c | 9 +++++---- > 1 file changed, 5 insertions(+), 4 deletions(-) > > diff --git a/arch/arm64/kernel/armv8_deprecated.c b/arch/arm64/kernel/armv8_deprecated.c > index 6875a16b09d2..fb0e7c7b2e20 100644 > --- a/arch/arm64/kernel/armv8_deprecated.c > +++ b/arch/arm64/kernel/armv8_deprecated.c > @@ -59,6 +59,7 @@ struct insn_emulation { > static LIST_HEAD(insn_emulation); > static int nr_insn_emulated __initdata; > static DEFINE_RAW_SPINLOCK(insn_emulation_lock); > +static DEFINE_MUTEX(insn_emulation_mutex); > > static void register_emulation_hooks(struct insn_emulation_ops *ops) > { > @@ -207,10 +208,10 @@ static int emulation_proc_handler(struct ctl_table *table, int write, > loff_t *ppos) > { > int ret = 0; > - struct insn_emulation *insn = (struct insn_emulation *) table->data; > + struct insn_emulation *insn = container_of(table->data, struct insn_emulation, current_mode); > enum insn_emulation_mode prev_mode = insn->current_mode; > > - table->data = &insn->current_mode; > + mutex_lock(&insn_emulation_mutex); > ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos); > > if (ret || !write || prev_mode == insn->current_mode) > @@ -223,7 +224,7 @@ static int emulation_proc_handler(struct ctl_table *table, int write, > update_insn_emulation_mode(insn, INSN_UNDEF); > } > ret: > - table->data = insn; > + mutex_unlock(&insn_emulation_mutex); > return ret; > } > > @@ -247,7 +248,7 @@ static void __init register_insn_emulation_sysctl(void) > sysctl->maxlen = sizeof(int); > > sysctl->procname = insn->ops->name; > - sysctl->data = insn; > + sysctl->data = &insn->current_mode; > sysctl->extra1 = &insn->min; > sysctl->extra2 = &insn->max; > sysctl->proc_handler = emulation_proc_handler; > -- > 2.34.1 > -- Lee Jones [李琼斯] Principal Technical Lead - Developer Services Linaro.org │ Open source software for Arm SoCs Follow Linaro: Facebook | Twitter | Blog