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SubjectRe: [PATCH 1/3] uprobes: Change write_opcode() to use FOLL_FORCE
* Oleg Nesterov <oleg@redhat.com> [2012-09-16 19:52:42]:

> write_opcode()->get_user_pages() needs FOLL_FORCE to ensure we can
> read the page even if the probed task did mprotect(PROT_NONE) after
> uprobe_register(). Without FOLL_WRITE, FOLL_FORCE doesn't have any
> side effect but allows to read the !VM_READ memory.
>
> Otherwiese the subsequent uprobe_unregister()->set_orig_insn() fails
> and we leak "int3". If that task does mprotect(PROT_READ | EXEC) and
> execute the probed insn later it will be killed.
>
> Note: in fact this is also needed for _register, see the next patch.
>
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>

Acked-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>

> ---
> kernel/events/uprobes.c | 2 +-
> 1 files changed, 1 insertions(+), 1 deletions(-)
>
> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index 14c2e99..fa1579a 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -221,7 +221,7 @@ static int write_opcode(struct arch_uprobe *auprobe, struct mm_struct *mm,
>
> retry:
> /* Read the page with vaddr into memory */
> - ret = get_user_pages(NULL, mm, vaddr, 1, 0, 0, &old_page, &vma);
> + ret = get_user_pages(NULL, mm, vaddr, 1, 0, 1, &old_page, &vma);
> if (ret <= 0)
> return ret;
>
> --
> 1.5.5.1
>



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