From 362f811793ff6cb4d209ab61d76cc4f841bb5e46 Mon Sep 17 00:00:00 2001 From: Gerd Hoffmann Date: Tue, 10 Oct 2017 16:13:21 +0200 Subject: [PATCH 1/4] vga: drop line_offset variable Signed-off-by: Gerd Hoffmann --- hw/display/vga.c | 7 +++---- 1 file changed, 3 insertions(+), 4 deletions(-) diff --git a/hw/display/vga.c b/hw/display/vga.c index ed24ef7076..bf774e3402 100644 --- a/hw/display/vga.c +++ b/hw/display/vga.c @@ -1464,7 +1464,7 @@ static void vga_draw_graphic(VGACommonState *s, int full_update) { DisplaySurface *surface = qemu_console_surface(s->con); int y1, y, update, linesize, y_start, double_scan, mask, depth; - int width, height, shift_control, line_offset, bwidth, bits; + int width, height, shift_control, bwidth, bits; ram_addr_t page0, page1; DirtyBitmapSnapshot *snap = NULL; int disp_width, multi_scan, multi_run; @@ -1614,7 +1614,6 @@ static void vga_draw_graphic(VGACommonState *s, int full_update) s->cursor_invalidate(s); } - line_offset = s->line_offset; #if 0 printf("w=%d h=%d v=%d line_offset=%d cr[0x09]=0x%02x cr[0x17]=0x%02x linecmp=%d sr[0x01]=0x%02x\n", width, height, v, line_offset, s->cr[9], s->cr[VGA_CRTC_MODE], @@ -1629,7 +1628,7 @@ static void vga_draw_graphic(VGACommonState *s, int full_update) if (!full_update) { ram_addr_t region_start = addr1; - ram_addr_t region_end = addr1 + line_offset * height; + ram_addr_t region_end = addr1 + s->line_offset * height; vga_sync_dirty_bitmap(s); if (s->line_compare < height) { /* split screen mode */ @@ -1681,7 +1680,7 @@ static void vga_draw_graphic(VGACommonState *s, int full_update) if (!multi_run) { mask = (s->cr[VGA_CRTC_MODE] & 3) ^ 3; if ((y1 & mask) == mask) - addr1 += line_offset; + addr1 += s->line_offset; y1++; multi_run = multi_scan; } else { From 28f77de26a4f9995458ddeb9d34bb06c0193bdc9 Mon Sep 17 00:00:00 2001 From: Gerd Hoffmann Date: Tue, 10 Oct 2017 16:13:22 +0200 Subject: [PATCH 2/4] vga: handle cirrus vbe mode wraparounds. Commit "3d90c62548 vga: stop passing pointers to vga_draw_line* functions" is incomplete. It doesn't handle the case that the vga rendering code tries to create a shared surface, i.e. a pixman image backed by vga video memory. That can not work in case the guest display wraps from end of video memory to the start. So force shadowing in that case. Also adjust the snapshot region calculation. Can trigger with cirrus only, when programming vbe modes using the bochs api (stdvga, also qxl and virtio-vga in vga compat mode) wrap arounds can't happen. Fixes: CVE-2017-13672 Fixes: 3d90c6254863693a6b13d918d2b8682e08bbc681 Cc: P J P Reported-by: David Buchanan Signed-off-by: Gerd Hoffmann Message-id: 20171010141323.14049-3-kraxel@redhat.com --- hw/display/vga.c | 28 +++++++++++++++++++++------- 1 file changed, 21 insertions(+), 7 deletions(-) diff --git a/hw/display/vga.c b/hw/display/vga.c index bf774e3402..1afceb6f16 100644 --- a/hw/display/vga.c +++ b/hw/display/vga.c @@ -1465,13 +1465,13 @@ static void vga_draw_graphic(VGACommonState *s, int full_update) DisplaySurface *surface = qemu_console_surface(s->con); int y1, y, update, linesize, y_start, double_scan, mask, depth; int width, height, shift_control, bwidth, bits; - ram_addr_t page0, page1; + ram_addr_t page0, page1, region_start, region_end; DirtyBitmapSnapshot *snap = NULL; int disp_width, multi_scan, multi_run; uint8_t *d; uint32_t v, addr1, addr; vga_draw_line_func *vga_draw_line = NULL; - bool share_surface; + bool share_surface, force_shadow = false; pixman_format_code_t format; #ifdef HOST_WORDS_BIGENDIAN bool byteswap = !s->big_endian_fb; @@ -1484,6 +1484,15 @@ static void vga_draw_graphic(VGACommonState *s, int full_update) s->get_resolution(s, &width, &height); disp_width = width; + region_start = (s->start_addr * 4); + region_end = region_start + s->line_offset * height; + if (region_end > s->vbe_size) { + /* wraps around (can happen with cirrus vbe modes) */ + region_start = 0; + region_end = s->vbe_size; + force_shadow = true; + } + shift_control = (s->gr[VGA_GFX_MODE] >> 5) & 3; double_scan = (s->cr[VGA_CRTC_MAX_SCAN] >> 7); if (shift_control != 1) { @@ -1523,7 +1532,7 @@ static void vga_draw_graphic(VGACommonState *s, int full_update) format = qemu_default_pixman_format(depth, !byteswap); if (format) { share_surface = dpy_gfx_check_format(s->con, format) - && !s->force_shadow; + && !s->force_shadow && !force_shadow; } else { share_surface = false; } @@ -1627,8 +1636,6 @@ static void vga_draw_graphic(VGACommonState *s, int full_update) y1 = 0; if (!full_update) { - ram_addr_t region_start = addr1; - ram_addr_t region_end = addr1 + s->line_offset * height; vga_sync_dirty_bitmap(s); if (s->line_compare < height) { /* split screen mode */ @@ -1651,10 +1658,17 @@ static void vga_draw_graphic(VGACommonState *s, int full_update) addr = (addr & ~0x8000) | ((y1 & 2) << 14); } update = full_update; - page0 = addr; - page1 = addr + bwidth - 1; + page0 = addr & s->vbe_size_mask; + page1 = (addr + bwidth - 1) & s->vbe_size_mask; if (full_update) { update = 1; + } else if (page1 < page0) { + /* scanline wraps from end of video memory to the start */ + assert(force_shadow); + update = memory_region_snapshot_get_dirty(&s->vram, snap, + page0, 0); + update |= memory_region_snapshot_get_dirty(&s->vram, snap, + page1, 0); } else { update = memory_region_snapshot_get_dirty(&s->vram, snap, page0, page1 - page0); From b0898b42ef099bc125db1fbf62b7f02b505ef3a2 Mon Sep 17 00:00:00 2001 From: Gerd Hoffmann Date: Tue, 10 Oct 2017 16:13:23 +0200 Subject: [PATCH 3/4] vga: add ram_addr_t cast Reported by Coverity. Fixes: CID 1381409 Signed-off-by: Gerd Hoffmann Message-id: 20171010141323.14049-4-kraxel@redhat.com --- hw/display/vga.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/hw/display/vga.c b/hw/display/vga.c index 1afceb6f16..1d19f6bc48 100644 --- a/hw/display/vga.c +++ b/hw/display/vga.c @@ -1485,7 +1485,7 @@ static void vga_draw_graphic(VGACommonState *s, int full_update) disp_width = width; region_start = (s->start_addr * 4); - region_end = region_start + s->line_offset * height; + region_end = region_start + (ram_addr_t)s->line_offset * height; if (region_end > s->vbe_size) { /* wraps around (can happen with cirrus vbe modes) */ region_start = 0; From eb38e1bc3740725ca29a535351de94107ec58d51 Mon Sep 17 00:00:00 2001 From: Gerd Hoffmann Date: Wed, 11 Oct 2017 10:43:14 +0200 Subject: [PATCH 4/4] cirrus: fix oob access in mode4and5 write functions Move dst calculation into the loop, so we apply the mask on each interation and will not overflow vga memory. Cc: Prasad J Pandit Reported-by: Niu Guoxiang Signed-off-by: Gerd Hoffmann Message-id: 20171011084314.21752-1-kraxel@redhat.com --- hw/display/cirrus_vga.c | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-) diff --git a/hw/display/cirrus_vga.c b/hw/display/cirrus_vga.c index b4d579857a..bc32bf1e39 100644 --- a/hw/display/cirrus_vga.c +++ b/hw/display/cirrus_vga.c @@ -2038,15 +2038,14 @@ static void cirrus_mem_writeb_mode4and5_8bpp(CirrusVGAState * s, unsigned val = mem_value; uint8_t *dst; - dst = s->vga.vram_ptr + (offset &= s->cirrus_addr_mask); for (x = 0; x < 8; x++) { + dst = s->vga.vram_ptr + ((offset + x) & s->cirrus_addr_mask); if (val & 0x80) { *dst = s->cirrus_shadow_gr1; } else if (mode == 5) { *dst = s->cirrus_shadow_gr0; } val <<= 1; - dst++; } memory_region_set_dirty(&s->vga.vram, offset, 8); } @@ -2060,8 +2059,8 @@ static void cirrus_mem_writeb_mode4and5_16bpp(CirrusVGAState * s, unsigned val = mem_value; uint8_t *dst; - dst = s->vga.vram_ptr + (offset &= s->cirrus_addr_mask); for (x = 0; x < 8; x++) { + dst = s->vga.vram_ptr + ((offset + 2 * x) & s->cirrus_addr_mask & ~1); if (val & 0x80) { *dst = s->cirrus_shadow_gr1; *(dst + 1) = s->vga.gr[0x11]; @@ -2070,7 +2069,6 @@ static void cirrus_mem_writeb_mode4and5_16bpp(CirrusVGAState * s, *(dst + 1) = s->vga.gr[0x10]; } val <<= 1; - dst += 2; } memory_region_set_dirty(&s->vga.vram, offset, 16); }