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Re: [Qemu-devel] [PATCH] cirrus: fix oob access issue
From: |
Gerd Hoffmann |
Subject: |
Re: [Qemu-devel] [PATCH] cirrus: fix oob access issue |
Date: |
Tue, 24 Jan 2017 13:29:58 +0100 |
> >>> if (pitch < 0) {
> >>> int64_t min = addr
> >>> - + ((int64_t)s->cirrus_blt_height-1) * pitch;
> >>> + + ((int64_t)s->cirrus_blt_height-1) * pitch
> >>> + - s->cirrus_blt_width;
> >>> int32_t max = addr
> >>> + s->cirrus_blt_width;
> >>> if (min < 0 || max > s->vga.vram_size) {
> >>>
> >>
> >> I believe this is incorrect. In this case (AFAIR), "addr" points to the
> >> left-most pixel (= lowest address) of the bottom line (= highest
> >> address).
> >
> > If I read the code correctly it is backwards *both* x and y axis, so
> > addr is the right-most pixel of the bottom line.
>
> What is "max" then? If "addr" is the right-most pixel of the bottom
> line, then "max" has the highest address just past the rectangle, and
> then adding anything non-negative to it makes no sense.
That is (with the patch applied) inconsistent indeed. We must either
subtract s->cirrus_blt_width from min (addr == right-most), or add it to
max (addr == left-most), but certainly not both.
> ... Really as I remember it from the downstream review, the pitch is
> negative (bottom-up), but the horizontal direction remains left to right.
Looking at cirrus_vga_rop.h I see:
- cirrus_bitblt_rop_fwd_*() increment src and dst while walking the
scanline, and
- cirrus_bitblt_rop_bkwd_*() decrement src and dst ...
I still think x axis goes backwards too and therefore addr is the
right-most pixel.
cheers,
Gerd
- [Qemu-devel] [PATCH] cirrus: fix oob access issue, Li Qiang, 2017/01/24
- Re: [Qemu-devel] [PATCH] cirrus: fix oob access issue, no-reply, 2017/01/24
- Re: [Qemu-devel] [PATCH] cirrus: fix oob access issue, Laszlo Ersek, 2017/01/24
- Re: [Qemu-devel] [PATCH] cirrus: fix oob access issue, Gerd Hoffmann, 2017/01/24
- Re: [Qemu-devel] [PATCH] cirrus: fix oob access issue, Laszlo Ersek, 2017/01/24
- Re: [Qemu-devel] [PATCH] cirrus: fix oob access issue, Laszlo Ersek, 2017/01/24
- Re: [Qemu-devel] [PATCH] cirrus: fix oob access issue,
Gerd Hoffmann <=
- Re: [Qemu-devel] [PATCH] cirrus: fix oob access issue, Wolfgang Bumiller, 2017/01/24
- Re: [Qemu-devel] [PATCH] cirrus: fix oob access issue, Laszlo Ersek, 2017/01/24
- Re: [Qemu-devel] [PATCH] cirrus: fix oob access issue, Li Qiang, 2017/01/24
- Re: [Qemu-devel] [PATCH] cirrus: fix oob access issue, Laszlo Ersek, 2017/01/24
- Re: [Qemu-devel] [PATCH] cirrus: fix oob access issue, Gerd Hoffmann, 2017/01/25
- Re: [Qemu-devel] [PATCH] cirrus: fix oob access issue, Gerd Hoffmann, 2017/01/25
- Re: [Qemu-devel] [PATCH] cirrus: fix oob access issue, Laszlo Ersek, 2017/01/25