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    SubjectRe: [PATCH] uprobes: ensure that uprobe->offset and ->ref_ctr_offset are properly aligned
    Hi Oleg,

    On Tue, May 5, 2020 at 12:47 AM Oleg Nesterov <oleg@redhat.com> wrote:
    >
    > uprobe_write_opcode() must not cross page boundary; prepare_uprobe()
    > relies on arch_uprobe_analyze_insn() which should validate "vaddr" but
    > some architectures (csky, s390, and sparc) don't do this.
    >
    > We can remove the BUG_ON() check in prepare_uprobe() and validate the
    > offset early in __uprobe_register(). The new IS_ALIGNED() check matches
    > the alignment check in arch_prepare_kprobe() on supported architectures,
    > so I think that all insns must be aligned to UPROBE_SWBP_INSN_SIZE.
    >
    > Another problem is __update_ref_ctr() which was wrong from the very
    > beginning, it can read/write outside of kmap'ed page unless "vaddr" is
    > aligned to sizeof(short), __uprobe_register() should check this too.
    >
    > Cc: stable@vger.kernel.org
    > Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
    > Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
    > Signed-off-by: Oleg Nesterov <oleg@redhat.com>
    > ---
    > kernel/events/uprobes.c | 16 ++++++++++++----
    > 1 file changed, 12 insertions(+), 4 deletions(-)
    >
    > diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
    > index ece7e13f6e4a..cc2095607c74 100644
    > --- a/kernel/events/uprobes.c
    > +++ b/kernel/events/uprobes.c
    > @@ -867,10 +867,6 @@ static int prepare_uprobe(struct uprobe *uprobe, struct file *file,
    > if (ret)
    > goto out;
    >
    > - /* uprobe_write_opcode() assumes we don't cross page boundary */
    > - BUG_ON((uprobe->offset & ~PAGE_MASK) +
    > - UPROBE_SWBP_INSN_SIZE > PAGE_SIZE);
    > -
    > smp_wmb(); /* pairs with the smp_rmb() in handle_swbp() */
    > set_bit(UPROBE_COPY_INSN, &uprobe->flags);
    >
    > @@ -1166,6 +1162,15 @@ static int __uprobe_register(struct inode *inode, loff_t offset,
    > if (offset > i_size_read(inode))
    > return -EINVAL;
    >
    > + /*
    > + * This ensures that copy_from_page(), copy_to_page() and
    > + * __update_ref_ctr() can't cross page boundary.
    > + */
    > + if (!IS_ALIGNED(offset, UPROBE_SWBP_INSN_SIZE))
    > + return -EINVAL;
    > + if (!IS_ALIGNED(ref_ctr_offset, sizeof(short)))
    > + return -EINVAL;
    > +
    > retry:
    > uprobe = alloc_uprobe(inode, offset, ref_ctr_offset);
    > if (!uprobe)
    > @@ -2014,6 +2019,9 @@ static int is_trap_at_addr(struct mm_struct *mm, unsigned long vaddr)
    > uprobe_opcode_t opcode;
    > int result;
    >
    > + if (WARN_ON_ONCE(!IS_ALIGNED(vaddr, UPROBE_SWBP_INSN_SIZE)))
    > + return -EINVAL;
    > +
    > pagefault_disable();
    > result = __get_user(opcode, (uprobe_opcode_t __user *)vaddr);
    > pagefault_enable();
    > --
    > 2.25.1.362.g51ebf55
    >
    >
    Looks good to me, thx.

    Reviewed-by: Guo Ren <guoren@kernel.org>

    --
    Best Regards
    Guo Ren

    ML: https://lore.kernel.org/linux-csky/

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