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From 90ded2892509c6c62140b907c7d036964cf312d5 Mon Sep 17 00:00:00 2001
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From: Gerd Hoffmann <kraxel@redhat.com>
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Date: Fri, 20 Oct 2017 11:06:18 +0200
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Subject: [PATCH 3/7] vga: handle cirrus vbe mode wraparounds.
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RH-Author: Gerd Hoffmann <kraxel@redhat.com>
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Message-id: <20171020110619.2541-11-kraxel@redhat.com>
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Patchwork-id: 77404
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O-Subject: [RHEL-7.5 qemu-kvm PATCH 10/11] vga: handle cirrus vbe mode wraparounds.
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Bugzilla: 1501295
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RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
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RH-Acked-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
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RH-Acked-by: Miroslav Rezanina <mrezanin@redhat.com>
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Commit "3d90c62548 vga: stop passing pointers to vga_draw_line*
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functions" is incomplete. It doesn't handle the case that the vga
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rendering code tries to create a shared surface, i.e. a pixman image
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backed by vga video memory. That can not work in case the guest display
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wraps from end of video memory to the start. So force shadowing in that
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case. Also adjust the snapshot region calculation.
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Can trigger with cirrus only, when programming vbe modes using the bochs
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api (stdvga, also qxl and virtio-vga in vga compat mode) wrap arounds
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can't happen.
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Fixes: CVE-2017-13672
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Fixes: 3d90c6254863693a6b13d918d2b8682e08bbc681
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Cc: P J P <ppandit@redhat.com>
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Reported-by: David Buchanan <d@vidbuchanan.co.uk>
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Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
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Message-id: 20171010141323.14049-3-kraxel@redhat.com
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(cherry picked from commit 28f77de26a4f9995458ddeb9d34bb06c0193bdc9)
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Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
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---
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hw/display/vga.c | 31 ++++++++++++++++++++++++-------
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1 file changed, 24 insertions(+), 7 deletions(-)
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diff --git a/hw/display/vga.c b/hw/display/vga.c
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index a343a0a..c40744f 100644
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--- a/hw/display/vga.c
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+++ b/hw/display/vga.c
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@@ -1505,12 +1505,12 @@ static void vga_draw_graphic(VGACommonState *s, int full_update)
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DisplaySurface *surface = qemu_console_surface(s->con);
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int y1, y, update, linesize, y_start, double_scan, mask, depth;
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int width, height, shift_control, bwidth, bits;
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- ram_addr_t page0, page1, page_min, page_max;
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+ ram_addr_t page0, page1, page_min, page_max, region_start, region_end;
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int disp_width, multi_scan, multi_run;
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uint8_t *d;
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uint32_t v, addr1, addr;
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vga_draw_line_func *vga_draw_line;
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- bool share_surface;
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+ bool share_surface, force_shadow = false;
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#if defined(TARGET_WORDS_BIGENDIAN)
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static const bool big_endian_fb = true;
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#else
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@@ -1530,6 +1530,15 @@ static void vga_draw_graphic(VGACommonState *s, int full_update)
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s->get_resolution(s, &width, &height);
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disp_width = width;
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+ region_start = (s->start_addr * 4);
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+ region_end = region_start + s->line_offset * height;
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+ if (region_end > s->vbe_size) {
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+ /* wraps around (can happen with cirrus vbe modes) */
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+ region_start = 0;
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+ region_end = s->vbe_size;
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+ force_shadow = true;
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+ }
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+
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shift_control = (s->gr[VGA_GFX_MODE] >> 5) & 3;
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double_scan = (s->cr[VGA_CRTC_MAX_SCAN] >> 7);
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if (shift_control != 1) {
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@@ -1560,7 +1569,7 @@ static void vga_draw_graphic(VGACommonState *s, int full_update)
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depth = s->get_bpp(s);
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- share_surface = (!s->force_shadow) &&
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+ share_surface = (!s->force_shadow) && !force_shadow &&
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( depth == 32 || (depth == 16 && !byteswap) );
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if (s->line_offset != s->last_line_offset ||
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disp_width != s->last_width ||
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@@ -1680,10 +1689,18 @@ static void vga_draw_graphic(VGACommonState *s, int full_update)
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addr = (addr & ~0x8000) | ((y1 & 2) << 14);
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}
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update = full_update;
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- page0 = addr;
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- page1 = addr + bwidth - 1;
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- update |= memory_region_get_dirty(&s->vram, page0, page1 - page0,
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- DIRTY_MEMORY_VGA);
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+ page0 = addr & s->vbe_size_mask;
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+ page1 = (addr + bwidth - 1) & s->vbe_size_mask;
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+ if (page1 < page0) {
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+ /* scanline wraps from end of video memory to the start */
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+ update |= memory_region_get_dirty(&s->vram, page0, 0,
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+ DIRTY_MEMORY_VGA);
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+ update |= memory_region_get_dirty(&s->vram, page1, 0,
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+ DIRTY_MEMORY_VGA);
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+ } else {
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+ update |= memory_region_get_dirty(&s->vram, page0, page1 - page0,
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+ DIRTY_MEMORY_VGA);
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+ }
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/* explicit invalidation for the hardware cursor */
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update |= (s->invalidated_y_table[y >> 5] >> (y & 0x1f)) & 1;
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if (update) {
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--
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1.8.3.1
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