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From af9348b27b8bc0c7033527220e7840f4b3209832 Mon Sep 17 00:00:00 2001
From: Jon Maloy <jmaloy@redhat.com>
Date: Tue, 6 Oct 2020 18:00:53 -0400
Subject: [PATCH 2/2] hw/core/loader: Fix possible crash in rom_copy()

RH-Author: Jon Maloy <jmaloy@redhat.com>
Message-id: <20201006180053.484822-2-jmaloy@redhat.com>
Patchwork-id: 98552
O-Subject: [RHEL-7.9.z qemu-kvm PATCH 1/1] hw/core/loader: Fix possible crash in rom_copy()
Bugzilla: 1842923
RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
RH-Acked-by: Markus Armbruster <armbru@redhat.com>
RH-Acked-by: Thomas Huth <thuth@redhat.com>

From: Thomas Huth <thuth@redhat.com>

Both, "rom->addr" and "addr" are derived from the binary image
that can be loaded with the "-kernel" paramer. The code in
rom_copy() then calculates:

    d = dest + (rom->addr - addr);

and uses "d" as destination in a memcpy() some lines later. Now with
bad kernel images, it is possible that rom->addr is smaller than addr,
thus "rom->addr - addr" gets negative and the memcpy() then tries to
copy contents from the image to a bad memory location. This could
maybe be used to inject code from a kernel image into the QEMU binary,
so we better fix it with an additional sanity check here.

Cc: qemu-stable@nongnu.org
Reported-by: Guangming Liu
Buglink: https://bugs.launchpad.net/qemu/+bug/1844635
Message-Id: <20190925130331.27825-1-thuth@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>

(cherry picked from commit e423455c4f23a1a828901c78fe6d03b7dde79319)
Signed-off-by: Jon Maloy <jmaloy@redhat.com>
Signed-off-by: Jon Maloy <jmaloy.redhat.com>
---
 hw/core/loader.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/hw/core/loader.c b/hw/core/loader.c
index 5a15449407..939d0855cb 100644
--- a/hw/core/loader.c
+++ b/hw/core/loader.c
@@ -841,7 +841,7 @@ int rom_copy(uint8_t *dest, hwaddr addr, size_t size)
         if (rom->addr + rom->romsize < addr) {
             continue;
         }
-        if (rom->addr > end) {
+        if (rom->addr > end || rom->addr < addr) {
             break;
         }
 
-- 
2.18.2