| Message ID | 20170519212636.30440-2-riel@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
* riel@redhat.com <riel@redhat.com> wrote: > From: Rik van Riel <riel@redhat.com> > > Introduce the get_random_canary function, which provides a random > unsigned long canary value with the first byte zeroed out on 64 > bit architectures, in order to mitigate non-terminated C string > overflows. > > Inspired by the "ascii armor" code in the old execshield patches, > and the current PaX/grsecurity code base. > > Signed-off-by: Rik van Riel <riel@redhat.com> > --- > include/linux/random.h | 20 ++++++++++++++++++++ > 1 file changed, 20 insertions(+) > > diff --git a/include/linux/random.h b/include/linux/random.h > index ed5c3838780d..765a992c6774 100644 > --- a/include/linux/random.h > +++ b/include/linux/random.h > @@ -57,6 +57,26 @@ static inline unsigned long get_random_long(void) > #endif > } > > +/* > + * On 64 bit architectures, protect against non-terminated C string overflows s/64 bit/64-bit > + * by zeroing out the first byte of the canary; this leaves 56 bits of entropy. > + */ > +#ifdef CONFIG_64BIT > +#ifdef __LITTLE_ENDIAN > +#define CANARY_MASK 0xffffffffffffff00UL > +#else /* big endian 64 bits */ > +#define CANARY_MASK 0x00ffffffffffffffUL > +#endif > +#else /* 32 bits */ > +#define CANARY_MASK 0xffffffffUL > +#endif > +static inline unsigned long get_random_canary(void) > +{ > + unsigned long val = get_random_long(); > + > + return val & CANARY_MASK; > +} Please separate function definitions from macros by a separate empty line. Also, a bit of structure and organization would make the macro easier to read: #ifdef CONFIG_64BIT # ifdef __LITTLE_ENDIAN # define CANARY_MASK 0xffffffffffffff00UL # else /* big endian, 64 bits: */ # define CANARY_MASK 0x00ffffffffffffffUL # endif #else /* 32 bits: */ # define CANARY_MASK 0x00000000ffffffffUL #endif Thanks, Ingo
diff --git a/include/linux/random.h b/include/linux/random.h index ed5c3838780d..765a992c6774 100644 --- a/include/linux/random.h +++ b/include/linux/random.h @@ -57,6 +57,26 @@ static inline unsigned long get_random_long(void) #endif } +/* + * On 64 bit architectures, protect against non-terminated C string overflows + * by zeroing out the first byte of the canary; this leaves 56 bits of entropy. + */ +#ifdef CONFIG_64BIT +#ifdef __LITTLE_ENDIAN +#define CANARY_MASK 0xffffffffffffff00UL +#else /* big endian 64 bits */ +#define CANARY_MASK 0x00ffffffffffffffUL +#endif +#else /* 32 bits */ +#define CANARY_MASK 0xffffffffUL +#endif +static inline unsigned long get_random_canary(void) +{ + unsigned long val = get_random_long(); + + return val & CANARY_MASK; +} + unsigned long randomize_page(unsigned long start, unsigned long range); u32 prandom_u32(void);