From: Jing Xiangfeng <jingxiangfeng@huawei.com>
To: Russell King - ARM Linux admin <linux@armlinux.org.uk>
Cc: kstewart@linuxfoundation.org, gustavo@embeddedor.com,
gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org,
linux-mm@kvack.org, ebiederm@xmission.com,
sakari.ailus@linux.intel.com, bhelgaas@google.com,
tglx@linutronix.de, linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH] arm: fix page faults in do_alignment
Date: Sat, 31 Aug 2019 09:49:45 +0800 [thread overview]
Message-ID: <5D69D239.2080908@huawei.com> (raw)
In-Reply-To: <20190830133522.GZ13294@shell.armlinux.org.uk>
On 2019/8/30 21:35, Russell King - ARM Linux admin wrote:
> On Fri, Aug 30, 2019 at 09:31:17PM +0800, Jing Xiangfeng wrote:
>> The function do_alignment can handle misaligned address for user and
>> kernel space. If it is a userspace access, do_alignment may fail on
>> a low-memory situation, because page faults are disabled in
>> probe_kernel_address.
>>
>> Fix this by using __copy_from_user stead of probe_kernel_address.
>>
>> Fixes: b255188 ("ARM: fix scheduling while atomic warning in alignment handling code")
>> Signed-off-by: Jing Xiangfeng <jingxiangfeng@huawei.com>
>
> NAK.
>
> The "scheduling while atomic warning in alignment handling code" is
> caused by fixing up the page fault while trying to handle the
> mis-alignment fault generated from an instruction in atomic context.
__might_sleep is called in the function __get_user which lead to that bug.
And that bug is triggered in a kernel space. Page fault can not be generated.
Right?
> Your patch re-introduces that bug.
>
>> ---
>> arch/arm/mm/alignment.c | 16 +++++++++++++---
>> 1 file changed, 13 insertions(+), 3 deletions(-)
>>
>> diff --git a/arch/arm/mm/alignment.c b/arch/arm/mm/alignment.c
>> index 04b3643..2ccabd3 100644
>> --- a/arch/arm/mm/alignment.c
>> +++ b/arch/arm/mm/alignment.c
>> @@ -774,6 +774,7 @@ static ssize_t alignment_proc_write(struct file *file, const char __user *buffer
>> unsigned long instr = 0, instrptr;
>> int (*handler)(unsigned long addr, unsigned long instr, struct pt_regs *regs);
>> unsigned int type;
>> + mm_segment_t fs;
>> unsigned int fault;
>> u16 tinstr = 0;
>> int isize = 4;
>> @@ -784,16 +785,22 @@ static ssize_t alignment_proc_write(struct file *file, const char __user *buffer
>>
>> instrptr = instruction_pointer(regs);
>>
>> + fs = get_fs();
>> + set_fs(KERNEL_DS);
>> if (thumb_mode(regs)) {
>> u16 *ptr = (u16 *)(instrptr & ~1);
>> - fault = probe_kernel_address(ptr, tinstr);
>> + fault = __copy_from_user(tinstr,
>> + (__force const void __user *)ptr,
>> + sizeof(tinstr));
>> tinstr = __mem_to_opcode_thumb16(tinstr);
>> if (!fault) {
>> if (cpu_architecture() >= CPU_ARCH_ARMv7 &&
>> IS_T32(tinstr)) {
>> /* Thumb-2 32-bit */
>> u16 tinst2 = 0;
>> - fault = probe_kernel_address(ptr + 1, tinst2);
>> + fault = __copy_from_user(tinst2,
>> + (__force const void __user *)(ptr+1),
>> + sizeof(tinst2));
>> tinst2 = __mem_to_opcode_thumb16(tinst2);
>> instr = __opcode_thumb32_compose(tinstr, tinst2);
>> thumb2_32b = 1;
>> @@ -803,10 +810,13 @@ static ssize_t alignment_proc_write(struct file *file, const char __user *buffer
>> }
>> }
>> } else {
>> - fault = probe_kernel_address((void *)instrptr, instr);
>> + fault = __copy_from_user(instr,
>> + (__force const void __user *)instrptr,
>> + sizeof(instr));
>> instr = __mem_to_opcode_arm(instr);
>> }
>>
>> + set_fs(fs);
>> if (fault) {
>> type = TYPE_FAULT;
>> goto bad_or_fault;
>> --
>> 1.8.3.1
>>
>>
>
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next prev parent reply other threads:[~2019-08-31 1:50 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-30 13:31 [PATCH] arm: fix page faults in do_alignment Jing Xiangfeng
2019-08-30 13:35 ` Russell King - ARM Linux admin
2019-08-30 13:48 ` Russell King - ARM Linux admin
2019-08-30 19:45 ` Eric W. Biederman
2019-08-30 20:30 ` Russell King - ARM Linux admin
2019-08-30 21:02 ` Eric W. Biederman
2019-08-30 22:29 ` Russell King - ARM Linux admin
2019-09-02 17:36 ` Eric W. Biederman
2019-09-04 2:17 ` Jing Xiangfeng
2019-09-06 15:17 ` Russell King - ARM Linux admin
2019-09-15 18:34 ` Russell King - ARM Linux admin
2019-09-16 14:31 ` Eric W. Biederman
2019-08-31 1:49 ` Jing Xiangfeng [this message]
2019-08-31 7:55 ` Russell King - ARM Linux admin
2019-08-31 9:16 ` Jing Xiangfeng
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