UBSAN detected a 64-bit shift in log2.h:__roundup_pow_of_two(): UBSAN: shift-out-of-bounds in ./include/linux/log2.h:57:13 shift exponent 64 is too large for 64-bit type 'long unsigned int'
This is during a call from mm/readahead.c:ondemand_readahead(), get_init_ra_size(), where the 'size' parameter must have been extremely large (or "negative"). fls() can legitimately return 32 or 64 when the MSbit is set in a 32-bit or 64-bit unsigned long. For these values, doing "1UL << shiftcout" is invalid or undefined, so catch when this happens. When the MSbit is 32 or 64, we cannot roundup to the next power of 2, so just return n (the input value), which is >= 0x8000...0000 and probably not a power of 2 (unless it is exactly 0x8000...0000). Signed-off-by: Randy Dunlap <[email protected]> Cc: Jens Axboe <[email protected]> Cc: Andrew Morton <[email protected]> Cc: Toralf Förster <[email protected]> Cc: [email protected] --- include/linux/log2.h | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) --- linux-5.10.1.orig/include/linux/log2.h +++ linux-5.10.1/include/linux/log2.h @@ -54,7 +54,17 @@ bool is_power_of_2(unsigned long n) static inline __attribute__((const)) unsigned long __roundup_pow_of_two(unsigned long n) { - return 1UL << fls_long(n - 1); + unsigned int lastset = fls_long(n - 1); /* this can be 64 or 32 */ + + /* + * for high bit set (64 or 32), we can neither round up nor + * make it a power or 2 + */ + if ((sizeof(n) == 4 && lastset == 32) || + (sizeof(n) == 8 && lastset == 64)) + return n; + + return 1UL << lastset; } /**
