GccSsp
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We will not rebuild the archive in one shot. So in the unlikely event that SSP will cause many regressions, we can immediately revert enabling it and just have to rebuild a relatively low number of packages. |
Launchpad Entry: https://launchpad.net/distros/ubuntu/+spec/gcc-ssp
Created: 2006-06-14 by MartinPitt
Contributors: MartinPitt
Packages affected: gcc-4.1, all
Summary
gcc 4.1 comes with SSP now, which is a nice technology to mitigate exploitability of many buffer overflows. This greatly enhances security in the time between publication of a vulnerability and the USN.
Rationale
A considerable percentage of arbitrary code execution vulnerabilities result from buffer overflows; about half of them occur due to overflowing a stack variable. While this does not avoid the necessity of issuing USNs, it provides effective zero-day protection for a subset of vulnerabilities, and since it is now in gcc upstream, it is very cheap for us to enable and support.
Use cases
- Pitti reads about a stack buffer overflow in Firefox. However, backporting the fix to our current stable release takes a while. Users of our stable release can live for a while with Firefox crashing when visiting a malicious web site, but they do not want to be subject to arbitrary code execution until an USN is published.
Scope
This affects all packages in all components.
Design
SSP provides a technology to stop exploitability of this class of vulnerabilities by (1) reordering stack variables and (2) adding a 'canary' (a random number) to the bottom of the stack, which is checked when the function is returned, so that attempts to overwrite the return pointer are detected and stopped.
SSP itself has been around for some years and thus has matured quite a bit, and many distros are using it by default already. Therefore this should not be a major risk, since we are merely catching up with existing technology.
Implementation
RedHat and gentoo are using SSP by default for years, so we do not expect much breakage potential. So we will build packages with SSP enabled right from the start in Edgy, so that we have much time to discover breakage. If it is not trivial to fix a package for SSP, we can disable it by building it with fno-stack-protector.
We will not rebuild the archive in one shot. So in the unlikely event that SSP will cause many regressions, we can immediately revert enabling it and just have to rebuild a relatively low number of packages.
testing
The following dapper packages have been tested with SSP enabled (built with gcc-4.1 and -fstack-protector under edgy):
perl |
ok |
python |
ok |
apache2 |
ok |
php5 |
ok |
postgresql-8.1 |
ok |
firefox |
ok |
mysql-dfsg-5.0 |
ok |
glib2.0 |
ok |
gtk+2.0 |
ok |
glibc |
a local build automatically uses SSP if it is available; needs testing |
xorg |
|
Before enabling SSP by default we will ensure that all those packages work flawlessly with SSP.
gcc changes
- Merge back libssp-dev into gcc, so that we do not have to add it as build dependency to packages.
Change gcc-4.1 to enable -fstack-protector by default.
GccSsp (last edited 2008-08-06 16:19:12 by localhost)