Messages in this thread | | | Subject | Re: [kernel-hardening] Re: [PATCH v1 0/2] Introduce the initify gcc plugin | From | Joe Perches <> | Date | Tue, 28 Jun 2016 16:54:09 -0700 |
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On Tue, 2016-06-28 at 18:07 -0400, Valdis.Kletnieks@vt.edu wrote: > On Tue, 28 Jun 2016 14:49:15 -0700, Joe Perches said: > > > > > Another potentially useful plugin, especially for embedded systems, > > would be to compress any string literal marked with > > > > __attribute__((format(printf, string-index,))) > > > > and decompress the compressed format on the stack in lib/vsprintf.c > > vsnprintf just before use. > Are there enough such strings in the kernel to make it worth the effort? > I'm assuming that the string literals in printk("some string here") are > automatically so marked?
Yes, that's the concept.
> Is there a minimum length under which the compression overhead actually > makes it larger?
No, compression would have to be possible, otherwise it'd be stored directly. Compression would use a special "compressed string" header with a 2 byte overhead and then stored with no trailing \0.
Something like struct compressed_format_header { u8 flag; /* Must be ASCII STX or "\b" */ u8 length; }
Depends on the config of course, but it could reduce total image size ~50k on an x86-32 defconfig
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