Re: [PATCH 2/3] x86/uprobes: Fix not using prefixes.nbytes for loop over prefixes.bytes

From: Masami Hiramatsu
Date: Wed Dec 02 2020 - 23:22:54 EST


On Wed, 2 Dec 2020 20:21:35 +0530
Srikar Dronamraju <srikar@xxxxxxxxxxxxxxxxxx> wrote:

> * Masami Hiramatsu <mhiramat@xxxxxxxxxx> [2020-12-02 17:51:16]:
>
> > Since the insn.prefixes.nbytes can be bigger than the size of
> > insn.prefixes.bytes[] when a same prefix is repeated, we have to
> > check whether the insn.prefixes.bytes[i] != 0 and i < 4 instead
> > of insn.prefixes.nbytes.
> >
> > Fixes: 2b1444983508 ("uprobes, mm, x86: Add the ability to install and remove uprobes breakpoints")
> > Cc: stable@xxxxxxxxxxxxxxx
> > Reported-by: Kees Cook <keescook@xxxxxxxxxxxx>
> > Signed-off-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
>
> Looks good to me.
>
> Reviewed-by: Srikar Dronamraju <srikar@xxxxxxxxxxxxxxxxxx>

Thanks Srikar!


>
> > ---
> > arch/x86/kernel/uprobes.c | 4 ++--
> > 1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
> > index 3fdaa042823d..bb3ea3705b99 100644
> > --- a/arch/x86/kernel/uprobes.c
> > +++ b/arch/x86/kernel/uprobes.c
> > @@ -257,7 +257,7 @@ static bool is_prefix_bad(struct insn *insn)
> > {
> > int i;
> >
> > - for (i = 0; i < insn->prefixes.nbytes; i++) {
> > + for (i = 0; insn->prefixes.bytes[i] && i < 4; i++) {
> > insn_attr_t attr;
> >
> > attr = inat_get_opcode_attribute(insn->prefixes.bytes[i]);
> > @@ -746,7 +746,7 @@ static int branch_setup_xol_ops(struct arch_uprobe *auprobe, struct insn *insn)
> > * Intel and AMD behavior differ in 64-bit mode: Intel ignores 66 prefix.
> > * No one uses these insns, reject any branch insns with such prefix.
> > */
> > - for (i = 0; i < insn->prefixes.nbytes; i++) {
> > + for (i = 0; insn->prefixes.bytes[i] && i < 4; i++) {
> > if (insn->prefixes.bytes[i] == 0x66)
> > return -ENOTSUPP;
> > }
> >
>
> --
> Thanks and Regards
> Srikar Dronamraju


--
Masami Hiramatsu <mhiramat@xxxxxxxxxx>