Re: [PATCH] hw/display/ati_2d: Fix buffer overflow in ati_2d_blt (CVE-2021-3638)

[Alexander Bulekov]

On 210906 2019, Philippe Mathieu-Daudé wrote:
> (Forgot to Cc Alex for eventual reproducer)

Here you go. Should we be fuzzing this on OSS-Fuzz?

============= 8< =============

/*
 * cat << EOF | ./qemu-system-i386 -display none -machine accel=qtest, -m \
 * 512M -device ati-vga,romfile= -nodefaults -qtest /dev/null -qtest stdio
 * outl 0xcf8 0x80001018
 * outl 0xcfc 0xe1000000
 * outl 0xcf8 0x80001004
 * outw 0xcfc 0x02
 * write 0xe10016c4 0x1 0x04
 * write 0xe10016e4 0x1 0x58
 * write 0xe1001438 0x4 0x0400001a
 * write 0xe100143c 0x4 0x01000015
 * EOF
 */
static void test_fuzz(void)
{
    QTestState *s = qtest_init(
        "-display none , -m 512M -device ati-vga,romfile= -nodefaults -qtest 
/dev/null");
    qtest_outl(s, 0xcf8, 0x80001018);
    qtest_outl(s, 0xcfc, 0xe1000000);
    qtest_outl(s, 0xcf8, 0x80001004);
    qtest_outw(s, 0xcfc, 0x02);
    qtest_bufwrite(s, 0xe10016c4, "\x04", 0x1);
    qtest_bufwrite(s, 0xe10016e4, "\x58", 0x1);
    qtest_bufwrite(s, 0xe1001438, "\x04\x00\x00\x1a", 0x4);
    qtest_bufwrite(s, 0xe100143c, "\x01\x00\x00\x15", 0x4);
    qtest_quit(s);
}

============= >8 =============
-Alex

> 
> On 9/6/21 6:44 PM, Mauro Matteo Cascella wrote:
> > On Mon, Sep 6, 2021 at 5:31 PM Philippe Mathieu-Daudé <philmd@redhat.com> 
> > wrote:
> >>
> >> When building QEMU with DEBUG_ATI defined then running with
> >> '-device ati-vga,romfile="" -d unimp,guest_errors -trace ati\*'
> >> we get:
> >>
> >>   ati_mm_write 4 0x16c0 DP_CNTL <- 0x1
> >>   ati_mm_write 4 0x146c DP_GUI_MASTER_CNTL <- 0x2
> >>   ati_mm_write 4 0x16c8 DP_MIX <- 0xff0000
> >>   ati_mm_write 4 0x16c4 DP_DATATYPE <- 0x2
> >>   ati_mm_write 4 0x224 CRTC_OFFSET <- 0x0
> >>   ati_mm_write 4 0x142c DST_PITCH_OFFSET <- 0xfe00000
> >>   ati_mm_write 4 0x1420 DST_Y <- 0x3fff
> >>   ati_mm_write 4 0x1410 DST_HEIGHT <- 0x3fff
> >>   ati_mm_write 4 0x1588 DST_WIDTH_X <- 0x3fff3fff
> >>   ati_2d_blt: vram:0x7fff5fa00000 addr:0 ds:0x7fff61273800 stride:2560 
> >> bpp:32 rop:0xff
> >>   ati_2d_blt: 0 0 0, 0 127 0, (0,0) -> (16383,16383) 16383x16383 > ^
> >>   ati_2d_blt: pixman_fill(dst:0x7fff5fa00000, stride:254, bpp:8, x:16383, 
> >> y:16383, w:16383, h:16383, xor:0xff000000)
> >>   Thread 3 "qemu-system-i38" received signal SIGSEGV, Segmentation fault.
> >>   (gdb) bt
> >>   #0  0x00007ffff7f62ce0 in sse2_fill.lto_priv () at 
> >> /lib64/libpixman-1.so.0
> >>   #1  0x00007ffff7f09278 in pixman_fill () at /lib64/libpixman-1.so.0
> >>   #2  0x0000555557b5a9af in ati_2d_blt (s=0x631000028800) at 
> >> hw/display/ati_2d.c:196
> >>   #3  0x0000555557b4b5a2 in ati_mm_write (opaque=0x631000028800, 
> >> addr=5512, data=1073692671, size=4) at hw/display/ati.c:843
> >>   #4  0x0000555558b90ec4 in memory_region_write_accessor 
> >> (mr=0x631000039cc0, addr=5512, ..., size=4, ...) at softmmu/memory.c:492
> >>
> >> Commit 584acf34cb0 ("ati-vga: Fix reverse bit blts") introduced
> >> the local dst_x and dst_y which adjust the (x, y) coordinates
> >> depending on the direction in the SRCCOPY ROP3 operation, but
> >> forgot to address the same issue for the PATCOPY, BLACKNESS and
> >> WHITENESS operations, which also call pixman_fill().
> >>
> >> Fix that now by using the adjusted coordinates in the pixman_fill
> >> call, and update the related debug printf().
> >>
> >> Reported-by: Qiang Liu <qiangliu@zju.edu.cn>
> >> Fixes: 584acf34cb0 ("ati-vga: Fix reverse bit blts")
> >> Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
> >> ---
> >>  hw/display/ati_2d.c | 6 +++---
> >>  1 file changed, 3 insertions(+), 3 deletions(-)
> >>
> >> diff --git a/hw/display/ati_2d.c b/hw/display/ati_2d.c
> >> index 4dc10ea7952..692bec91de4 100644
> >> --- a/hw/display/ati_2d.c
> >> +++ b/hw/display/ati_2d.c
> >> @@ -84,7 +84,7 @@ void ati_2d_blt(ATIVGAState *s)
> >>      DPRINTF("%d %d %d, %d %d %d, (%d,%d) -> (%d,%d) %dx%d %c %c\n",
> >>              s->regs.src_offset, s->regs.dst_offset, 
> >> s->regs.default_offset,
> >>              s->regs.src_pitch, s->regs.dst_pitch, s->regs.default_pitch,
> >> -            s->regs.src_x, s->regs.src_y, s->regs.dst_x, s->regs.dst_y,
> >> +            s->regs.src_x, s->regs.src_y, dst_x, dst_y,
> >>              s->regs.dst_width, s->regs.dst_height,
> >>              (s->regs.dp_cntl & DST_X_LEFT_TO_RIGHT ? '>' : '<'),
> >>              (s->regs.dp_cntl & DST_Y_TOP_TO_BOTTOM ? 'v' : '^'));
> >> @@ -180,11 +180,11 @@ void ati_2d_blt(ATIVGAState *s)
> >>          dst_stride /= sizeof(uint32_t);
> >>          DPRINTF("pixman_fill(%p, %d, %d, %d, %d, %d, %d, %x)\n",
> >>                  dst_bits, dst_stride, bpp,
> >> -                s->regs.dst_x, s->regs.dst_y,
> >> +                dst_x, dst_y,
> >>                  s->regs.dst_width, s->regs.dst_height,
> >>                  filler);
> >>          pixman_fill((uint32_t *)dst_bits, dst_stride, bpp,
> >> -                    s->regs.dst_x, s->regs.dst_y,
> >> +                    dst_x, dst_y,
> >>                      s->regs.dst_width, s->regs.dst_height,
> >>                      filler);
> >>          if (dst_bits >= s->vga.vram_ptr + s->vga.vbe_start_addr &&
> >> --
> >> 2.31.1
> >>
> > 
> > Tested-by: Mauro Matteo Cascella <mcascell@redhat.com>
> 
> Thanks. I wouldn't be surprise if we get another CVE in this code /
> file / function ASAP this patch get merged... The code calls for a
> rewrite, as per this function comment in its header:
> 
> void ati_2d_blt(ATIVGAState *s)
> {
>     /* FIXME it is probably more complex than this and may need to be */
>     /* rewritten but for now as a start just to get some output: */
> 
> Regards,
> 
> Phil.
> 
>