tree dfd92cd0eca288962b0997acc95e5d1d22f19e09
parent 361d5397355276e3007825cc17217c1e4d4320f7
author Helge Deller <deller@gmx.de> 1689575837 +0200
committer Helge Deller <deller@gmx.de> 1689705725 +0200

linux-user: Fix qemu brk() to not zero bytes on current page

The qemu brk() implementation is too aggressive and cleans remaining bytes
on the current page above the last brk address.

But some existing applications are buggy and read/write bytes above their
current heap address. On a phyiscal machine this does not trigger a
runtime error as long as the access happens on the same page. Additionally
the Linux kernel allocates only full pages and does no zeroing on already
allocated pages, even if the brk address is lowered.

Fix qemu to behave the same way as the kernel does. Do not touch already
allocated pages, and - when running with different page sizes of guest and
host - zero out only those memory areas where the host page size is bigger
than the guest page size.

Signed-off-by: Helge Deller <deller@gmx.de>
Tested-by: "Markus F.X.J. Oberhumer" <markus@oberhumer.com>
Fixes: 86f04735ac ("linux-user: Fix brk() to release pages")
Cc: qemu-stable@nongnu.org
Buglink: https://github.com/upx/upx/issues/683