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SubjectRe: [PATCH] arm: fix page faults in do_alignment
Please fix your email.

jingxiangfeng@huawei.com
host mx7.huawei.com [168.195.93.46]
SMTP error from remote mail server after pipelined DATA:
554 5.7.1 spf check result is none

SPF is *not* required for email.

If you wish to impose such restrictions on email, then I reserve the
right to ignore your patches until this issue is resolved! ;)

On Fri, Aug 30, 2019 at 02:35:22PM +0100, 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.
>
> 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
> >
> >
>
> --
> RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
> FTTC broadband for 0.8mile line in suburbia: sync at 12.1Mbps down 622kbps up
> According to speedtest.net: 11.9Mbps down 500kbps up
>
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
>

--
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTC broadband for 0.8mile line in suburbia: sync at 12.1Mbps down 622kbps up
According to speedtest.net: 11.9Mbps down 500kbps up

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