[SeaBIOS] [PATCH] optionrom: disallow int19 redirect for pnp roms.

[Gerd Hoffmann]

Check whenever pnp roms attempt to redirect int19, and in case it does
log a message and undo the redirect.

A pnp rom should not need this, we have BEVs and BCVs for that.
Nevertheless there are roms in the wild which are redirecting int19.
At least some BIOS implementations for physical hardware have a config
option in the setup to allow/disallow int19 redirections, so just not
allowing this seems to be the way to deal with this situation.

Buglink: https://bugzilla.redhat.com//show_bug.cgi?id=1642135
Signed-off-by: Gerd Hoffmann <kraxel at redhat.com>
---
 src/optionroms.c | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/src/optionroms.c b/src/optionroms.c
index fc992f649f..4ec5504ca9 100644
--- a/src/optionroms.c
+++ b/src/optionroms.c
@@ -8,6 +8,7 @@
 #include "bregs.h" // struct bregs
 #include "config.h" // CONFIG_*
 #include "farptr.h" // FLATPTR_TO_SEG
+#include "biosvar.h" // GET_IVT
 #include "hw/pci.h" // pci_config_readl
 #include "hw/pcidevice.h" // foreachpci
 #include "hw/pci_ids.h" // PCI_CLASS_DISPLAY_VGA
@@ -136,9 +137,24 @@ init_optionrom(struct rom_header *rom, u16 bdf, int isvga)
 
     tpm_option_rom(newrom, rom->size * 512);
 
-    if (isvga || get_pnp_rom(newrom))
+    struct pnp_data *pnp = get_pnp_rom(newrom);
+    if (isvga || pnp) {
+        struct segoff_s old19, new19;
         // Only init vga and PnP roms here.
+        old19 = GET_IVT(0x19);
         callrom(newrom, bdf);
+        new19 = GET_IVT(0x19);
+        if (old19.seg != new19.seg ||
+            old19.offset != new19.offset) {
+            dprintf(1, "WARNING! rom tried to hijack int19 "
+                    "(vec %04x:%04x, pnp %s, bev %s, bvc %s)\n",
+                    new19.seg, new19.offset,
+                    pnp             ? "yes" : "no",
+                    pnp && pnp->bev ? "yes" : "no",
+                    pnp && pnp->bcv ? "yes" : "no");
+            SET_IVT(0x19, old19);
+        }
+    }
 
     return rom_confirm(newrom->size * 512);
 }
-- 
2.9.3