[qemu-xen stable-4.13] hw/core/loader: Fix possible crash in rom_copy()

[patchbot@xxxxxxx]

commit aae0faa5d3bee91c66dc4c1543190f55a242771e
Author:     Thomas Huth <thuth@xxxxxxxxxx>
AuthorDate: Wed Sep 25 14:16:43 2019 +0200
Commit:     Michael Roth <mdroth@xxxxxxxxxxxxxxxxxx>
CommitDate: Mon Nov 4 08:10:48 2019 -0600

    hw/core/loader: Fix possible crash in rom_copy()
    
    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@xxxxxxxxxx
    Reported-by: Guangming Liu
    Buglink: https://bugs.launchpad.net/qemu/+bug/1844635
    Message-Id: <20190925130331.27825-1-thuth@xxxxxxxxxx>
    Reviewed-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
    Signed-off-by: Thomas Huth <thuth@xxxxxxxxxx>
    (cherry picked from commit e423455c4f23a1a828901c78fe6d03b7dde79319)
    Signed-off-by: Michael Roth <mdroth@xxxxxxxxxxxxxxxxxx>
---
 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 425bf69a99..838a34174a 100644
--- a/hw/core/loader.c
+++ b/hw/core/loader.c
@@ -1242,7 +1242,7 @@ 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;
         }
 
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