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SubjectRe: [PATCH 2/2] nds32: use get_kernel_nofault in dump_mem
On Mon, Jul 20, 2020 at 01:44:48PM +0200, Christoph Hellwig wrote:
> Use the proper get_kernel_nofault helper to access an unsafe kernel
> pointer without faulting instead of playing with set_fs and get_user.
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
> arch/nds32/kernel/traps.c | 15 +++------------
> 1 file changed, 3 insertions(+), 12 deletions(-)
>
> diff --git a/arch/nds32/kernel/traps.c b/arch/nds32/kernel/traps.c
> index b66f889bc6df9b..ee0d9ae192a504 100644
> --- a/arch/nds32/kernel/traps.c
> +++ b/arch/nds32/kernel/traps.c
> @@ -25,17 +25,8 @@ extern void show_pte(struct mm_struct *mm, unsigned long addr);
> void dump_mem(const char *lvl, unsigned long bottom, unsigned long top)
> {
> unsigned long first;
> - mm_segment_t fs;
> int i;
>
> - /*
> - * We need to switch to kernel mode so that we can use __get_user
> - * to safely read from kernel space. Note that we now dump the
> - * code first, just in case the backtrace kills us.
> - */
> - fs = get_fs();
> - set_fs(KERNEL_DS);
> -
> pr_emerg("%s(0x%08lx to 0x%08lx)\n", lvl, bottom, top);
>
> for (first = bottom & ~31; first < top; first += 32) {
> @@ -48,7 +39,9 @@ void dump_mem(const char *lvl, unsigned long bottom, unsigned long top)
> for (p = first, i = 0; i < 8 && p < top; i++, p += 4) {
> if (p >= bottom && p < top) {
> unsigned long val;
> - if (__get_user(val, (unsigned long *)p) == 0)
> +
> + if (get_kernel_nofault(val,
> + (unsigned long *)p) == 0)
> sprintf(str + i * 9, " %08lx", val);
> else
> sprintf(str + i * 9, " ????????");
> @@ -56,8 +49,6 @@ void dump_mem(const char *lvl, unsigned long bottom, unsigned long top)
> }
> pr_emerg("%s%04lx:%s\n", lvl, first & 0xffff, str);
> }
> -
> - set_fs(fs);
> }
>
> EXPORT_SYMBOL(dump_mem);
> --
> 2.27.0
>
Hi Christoph,

Thank you!
Acked-by: Nick Hu <nickhu@andestech.com>

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