• Daniel Cashman's avatar
    drivers: char: random: add get_random_long() · ec9ee4ac
    Daniel Cashman authored
    Commit d07e2259 ("mm: mmap: add new /proc tunable for mmap_base
    ASLR") added the ability to choose from a range of values to use for
    entropy count in generating the random offset to the mmap_base address.
    
    The maximum value on this range was set to 32 bits for 64-bit x86
    systems, but this value could be increased further, requiring more than
    the 32 bits of randomness provided by get_random_int(), as is already
    possible for arm64.  Add a new function: get_random_long() which more
    naturally fits with the mmap usage of get_random_int() but operates
    exactly the same as get_random_int().
    
    Also, fix the shifting constant in mmap_rnd() to be an unsigned long so
    that values greater than 31 bits generate an appropriate mask without
    overflow.  This is especially important on x86, as its shift instruction
    uses a 5-bit mask for the shift operand, which meant that any value for
    mmap_rnd_bits over 31 acts as a no-op and effectively disables mmap_base
    randomization.
    
    Finally, replace calls to get_random_int() with get_random_long() where
    appropriate.
    
    This patch (of 2):
    
    Add get_random_long().
    Signed-off-by: default avatarDaniel Cashman <dcashman@android.com>
    Acked-by: default avatarKees Cook <keescook@chromium.org>
    Cc: "Theodore Ts'o" <tytso@mit.edu>
    Cc: Arnd Bergmann <arnd@arndb.de>
    Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    Cc: Catalin Marinas <catalin.marinas@arm.com>
    Cc: Will Deacon <will.deacon@arm.com>
    Cc: Ralf Baechle <ralf@linux-mips.org>
    Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
    Cc: Paul Mackerras <paulus@samba.org>
    Cc: Michael Ellerman <mpe@ellerman.id.au>
    Cc: David S. Miller <davem@davemloft.net>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: Ingo Molnar <mingo@redhat.com>
    Cc: H. Peter Anvin <hpa@zytor.com>
    Cc: Al Viro <viro@zeniv.linux.org.uk>
    Cc: Nick Kralevich <nnk@google.com>
    Cc: Jeff Vander Stoep <jeffv@google.com>
    Cc: Mark Salyzyn <salyzyn@android.com>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    ec9ee4ac
random.c 55.4 KB