Date: Sat, 14 Jan 2017 11:03:14 +0100 From: "PaX Team" <pageexec@...email.hu> To: kernel-hardening@...ts.openwall.com, Kees Cook <keescook@...omium.org> CC: Emese Revfy <re.emese@...il.com>, "AKASHI, Takahiro" <takahiro.akashi@...aro.org>, Mark Rutland <mark.rutland@....com>, park jinbum <jinb.park7@...il.com>, Daniel Micay <danielmicay@...il.com>, linux-kernel@...r.kernel.org, spender@...ecurity.net Subject: Re: [PATCH] gcc-plugins: Add structleak for more stack initialization On 13 Jan 2017 at 14:02, Kees Cook wrote: > This plugin detects any structures that contain __user attributes and > makes sure it is being fulling initialized so that a specific class of > information exposure is eliminated. (For example, the exposure of siginfo > in CVE-2013-2141 would have been blocked by this plugin.) why the conditional? the plugin was specifically written to block that bug and block it did ;). > +config GCC_PLUGIN_STRUCTLEAK > + bool "Force initialization of variables containing userspace addresses" > + depends on GCC_PLUGINS > + help > + This plugin zero-initializes any structures that containing a > + __user attribute. This can prevent some classes of information > + exposures. i see that you completely ditched the description in PaX, is there a reason for it? your text isn't correct as is because - the __user attribute (which is an implementation choice, see below) doesn't apply to structures but pointers only (as it does for sparse IIRC) - a structure is a type, but the plugin initializes variables, not types (the latter makes little sense) - the plugin doesn't initialize 'any structures' (well, variables), only locals and only at function scope (subject to further evolution as discussed earlier). > +config GCC_PLUGIN_STRUCTLEAK_VERBOSE > + bool "Report initialized variables" > + depends on GCC_PLUGIN_STRUCTLEAK > + depends on !COMPILE_TEST > + help > + This option will cause a warning to be printed each time the > + structleak plugin finds a variable it thinks needs to be > + initialized. Since not all existing initializers are detected > + by the plugin, this can produce false positive warnings. there are no false positives, a variable either has a constructor or it does not ;) > +/* unused C type flag in all versions 4.5-6 */ > +#define TYPE_USERSPACE(TYPE) TYPE_LANG_FLAG_5(TYPE) FYI, this is a sort of abuse/hack of tree flags and should not be implemented this way in the upstream kernel as it's a finite resource and needs careful verification against all supported gcc versions (these flags are meant for language fronteds, i kinda got lucky to have a few of them unusued but it's not a robust future-proof approach). instead an attribute should be used to mark these types. whether that can/should be __user itself is a good question since that's another hack where the plugin 'hijacks' a sparse address space atttribute (for which gcc 4.6+ has its own facilities and that the checker gcc plugin makes use of thus it's not compatible with structleak as is).
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