X-Git-Url: https://git.saurik.com/apple/xnu.git/blobdiff_plain/d1ecb069dfe24481e4a83f44cb5217a2b06746d7..eb6b6ca394357805f2bdba989abae309f718b4d8:/bsd/dev/random/randomdev.c?ds=sidebyside diff --git a/bsd/dev/random/randomdev.c b/bsd/dev/random/randomdev.c index c081bd209..7e5e10e3e 100644 --- a/bsd/dev/random/randomdev.c +++ b/bsd/dev/random/randomdev.c @@ -2,7 +2,7 @@ * Copyright (c) 1999-2009 Apple, Inc. All rights reserved. * * @APPLE_OSREFERENCE_LICENSE_HEADER_START@ - * + * * This file contains Original Code and/or Modifications of Original Code * as defined in and that are subject to the Apple Public Source License * Version 2.0 (the 'License'). You may not use this file except in @@ -11,10 +11,10 @@ * unlawful or unlicensed copies of an Apple operating system, or to * circumvent, violate, or enable the circumvention or violation of, any * terms of an Apple operating system software license agreement. - * + * * Please obtain a copy of the License at * http://www.opensource.apple.com/apsl/ and read it before using this file. - * + * * The Original Code and all software distributed under the License are * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES, @@ -22,20 +22,10 @@ * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT. * Please see the License for the specific language governing rights and * limitations under the License. - * + * * @APPLE_OSREFERENCE_LICENSE_HEADER_END@ */ -/* - WARNING! WARNING! WARNING! WARNING! WARNING! WARNING! WARNING! WARNING! WARNING! - - THIS FILE IS NEEDED TO PASS FIPS ACCEPTANCE FOR THE RANDOM NUMBER GENERATOR. - IF YOU ALTER IT IN ANY WAY, WE WILL NEED TO GO THOUGH FIPS ACCEPTANCE AGAIN, - AN OPERATION THAT IS VERY EXPENSIVE AND TIME CONSUMING. IN OTHER WORDS, - DON'T MESS WITH THIS FILE. - - WARNING! WARNING! WARNING! WARNING! WARNING! WARNING! WARNING! WARNING! WARNING! -*/ #include #include @@ -46,23 +36,23 @@ #include #include #include -#include +#include #include #include #include +#include #include #include -#include #include +#include #include -#include - -#include "fips_sha1.h" #define RANDOM_MAJOR -1 /* let the kernel pick the device number */ +#define RANDOM_MINOR 0 +#define URANDOM_MINOR 1 d_ioctl_t random_ioctl; @@ -72,308 +62,22 @@ d_ioctl_t random_ioctl; */ static struct cdevsw random_cdevsw = { - random_open, /* open */ - random_close, /* close */ - random_read, /* read */ - random_write, /* write */ - random_ioctl, /* ioctl */ + random_open, /* open */ + random_close, /* close */ + random_read, /* read */ + random_write, /* write */ + random_ioctl, /* ioctl */ (stop_fcn_t *)nulldev, /* stop */ (reset_fcn_t *)nulldev, /* reset */ - NULL, /* tty's */ - eno_select, /* select */ - eno_mmap, /* mmap */ - eno_strat, /* strategy */ - eno_getc, /* getc */ - eno_putc, /* putc */ - 0 /* type */ -}; - - -/* - WARNING! WARNING! WARNING! WARNING! WARNING! WARNING! WARNING! WARNING! WARNING! - - ANY CODE PROTECTED UNDER "#ifdef __arm__" IS SERIOUSLY SUPPOSED TO BE THERE! - IF YOU REMOVE ARM CODE, RANDOM WILL NOT MEAN ANYTHING FOR iPHONES ALL OVER. - PLEASE DON'T TOUCH __arm__ CODE IN THIS FILE! - - WARNING! WARNING! WARNING! WARNING! WARNING! WARNING! WARNING! WARNING! WARNING! -*/ - - -/* Used to detect whether we've already been initialized */ -static int gRandomInstalled = 0; -static PrngRef gPrngRef; -static int gRandomError = 1; -static lck_grp_t *gYarrowGrp; -static lck_attr_t *gYarrowAttr; -static lck_grp_attr_t *gYarrowGrpAttr; -static lck_mtx_t *gYarrowMutex = 0; - -#define RESEED_TICKS 50 /* how long a reseed operation can take */ - - -typedef u_int8_t BlockWord; -enum {kBSize = 20}; -typedef BlockWord Block[kBSize]; -enum {kBlockSize = sizeof(Block)}; - -/* define prototypes to keep the compiler happy... */ - -void add_blocks(Block a, Block b, BlockWord carry); -void fips_initialize(void); -void random_block(Block b, int addOptional); -u_int32_t CalculateCRC(u_int8_t* buffer, size_t length); - -/* - * Get 120 bits from yarrow - */ - -/* - * add block b to block a - */ -void -add_blocks(Block a, Block b, BlockWord carry) -{ - int i = kBlockSize - 1; - while (i >= 0) - { - u_int32_t c = (u_int32_t)carry + - (u_int32_t)a[i] + - (u_int32_t)b[i]; - a[i] = c & 0xff; - carry = c >> 8; - i -= 1; - } -} - - - -static char zeros[(512 - kBSize * 8) / 8]; -static Block g_xkey; -static Block g_random_data; -static int g_bytes_used; -static unsigned char g_SelfTestInitialized = 0; -static u_int32_t gLastBlockChecksum; - -static const u_int32_t g_crc_table[] = -{ - 0x00000000, 0x77073096, 0xEE0E612C, 0x990951BA, 0x076DC419, 0x706AF48F, 0xE963A535, 0x9E6495A3, - 0x0EDB8832, 0x79DCB8A4, 0xE0D5E91E, 0x97D2D988, 0x09B64C2B, 0x7EB17CBD, 0xE7B82D07, 0x90BF1D91, - 0x1DB71064, 0x6AB020F2, 0xF3B97148, 0x84BE41DE, 0x1ADAD47D, 0x6DDDE4EB, 0xF4D4B551, 0x83D385C7, - 0x136C9856, 0x646BA8C0, 0xFD62F97A, 0x8A65C9EC, 0x14015C4F, 0x63066CD9, 0xFA0F3D63, 0x8D080DF5, - 0x3B6E20C8, 0x4C69105E, 0xD56041E4, 0xA2677172, 0x3C03E4D1, 0x4B04D447, 0xD20D85FD, 0xA50AB56B, - 0x35B5A8FA, 0x42B2986C, 0xDBBBC9D6, 0xACBCF940, 0x32D86CE3, 0x45DF5C75, 0xDCD60DCF, 0xABD13D59, - 0x26D930AC, 0x51DE003A, 0xC8D75180, 0xBFD06116, 0x21B4F4B5, 0x56B3C423, 0xCFBA9599, 0xB8BDA50F, - 0x2802B89E, 0x5F058808, 0xC60CD9B2, 0xB10BE924, 0x2F6F7C87, 0x58684C11, 0xC1611DAB, 0xB6662D3D, - 0x76DC4190, 0x01DB7106, 0x98D220BC, 0xEFD5102A, 0x71B18589, 0x06B6B51F, 0x9FBFE4A5, 0xE8B8D433, - 0x7807C9A2, 0x0F00F934, 0x9609A88E, 0xE10E9818, 0x7F6A0DBB, 0x086D3D2D, 0x91646C97, 0xE6635C01, - 0x6B6B51F4, 0x1C6C6162, 0x856530D8, 0xF262004E, 0x6C0695ED, 0x1B01A57B, 0x8208F4C1, 0xF50FC457, - 0x65B0D9C6, 0x12B7E950, 0x8BBEB8EA, 0xFCB9887C, 0x62DD1DDF, 0x15DA2D49, 0x8CD37CF3, 0xFBD44C65, - 0x4DB26158, 0x3AB551CE, 0xA3BC0074, 0xD4BB30E2, 0x4ADFA541, 0x3DD895D7, 0xA4D1C46D, 0xD3D6F4FB, - 0x4369E96A, 0x346ED9FC, 0xAD678846, 0xDA60B8D0, 0x44042D73, 0x33031DE5, 0xAA0A4C5F, 0xDD0D7CC9, - 0x5005713C, 0x270241AA, 0xBE0B1010, 0xC90C2086, 0x5768B525, 0x206F85B3, 0xB966D409, 0xCE61E49F, - 0x5EDEF90E, 0x29D9C998, 0xB0D09822, 0xC7D7A8B4, 0x59B33D17, 0x2EB40D81, 0xB7BD5C3B, 0xC0BA6CAD, - 0xEDB88320, 0x9ABFB3B6, 0x03B6E20C, 0x74B1D29A, 0xEAD54739, 0x9DD277AF, 0x04DB2615, 0x73DC1683, - 0xE3630B12, 0x94643B84, 0x0D6D6A3E, 0x7A6A5AA8, 0xE40ECF0B, 0x9309FF9D, 0x0A00AE27, 0x7D079EB1, - 0xF00F9344, 0x8708A3D2, 0x1E01F268, 0x6906C2FE, 0xF762575D, 0x806567CB, 0x196C3671, 0x6E6B06E7, - 0xFED41B76, 0x89D32BE0, 0x10DA7A5A, 0x67DD4ACC, 0xF9B9DF6F, 0x8EBEEFF9, 0x17B7BE43, 0x60B08ED5, - 0xD6D6A3E8, 0xA1D1937E, 0x38D8C2C4, 0x4FDFF252, 0xD1BB67F1, 0xA6BC5767, 0x3FB506DD, 0x48B2364B, - 0xD80D2BDA, 0xAF0A1B4C, 0x36034AF6, 0x41047A60, 0xDF60EFC3, 0xA867DF55, 0x316E8EEF, 0x4669BE79, - 0xCB61B38C, 0xBC66831A, 0x256FD2A0, 0x5268E236, 0xCC0C7795, 0xBB0B4703, 0x220216B9, 0x5505262F, - 0xC5BA3BBE, 0xB2BD0B28, 0x2BB45A92, 0x5CB36A04, 0xC2D7FFA7, 0xB5D0CF31, 0x2CD99E8B, 0x5BDEAE1D, - 0x9B64C2B0, 0xEC63F226, 0x756AA39C, 0x026D930A, 0x9C0906A9, 0xEB0E363F, 0x72076785, 0x05005713, - 0x95BF4A82, 0xE2B87A14, 0x7BB12BAE, 0x0CB61B38, 0x92D28E9B, 0xE5D5BE0D, 0x7CDCEFB7, 0x0BDBDF21, - 0x86D3D2D4, 0xF1D4E242, 0x68DDB3F8, 0x1FDA836E, 0x81BE16CD, 0xF6B9265B, 0x6FB077E1, 0x18B74777, - 0x88085AE6, 0xFF0F6A70, 0x66063BCA, 0x11010B5C, 0x8F659EFF, 0xF862AE69, 0x616BFFD3, 0x166CCF45, - 0xA00AE278, 0xD70DD2EE, 0x4E048354, 0x3903B3C2, 0xA7672661, 0xD06016F7, 0x4969474D, 0x3E6E77DB, - 0xAED16A4A, 0xD9D65ADC, 0x40DF0B66, 0x37D83BF0, 0xA9BCAE53, 0xDEBB9EC5, 0x47B2CF7F, 0x30B5FFE9, - 0xBDBDF21C, 0xCABAC28A, 0x53B39330, 0x24B4A3A6, 0xBAD03605, 0xCDD70693, 0x54DE5729, 0x23D967BF, - 0xB3667A2E, 0xC4614AB8, 0x5D681B02, 0x2A6F2B94, 0xB40BBE37, 0xC30C8EA1, 0x5A05DF1B, 0x2D02EF8D, + NULL, /* tty's */ + eno_select, /* select */ + eno_mmap, /* mmap */ + eno_strat, /* strategy */ + eno_getc, /* getc */ + eno_putc, /* putc */ + 0 /* type */ }; -/* - * Setup for fips compliance - */ - -/* - * calculate a crc-32 checksum - */ -u_int32_t CalculateCRC(u_int8_t* buffer, size_t length) -{ - u_int32_t crc = 0; - - size_t i; - for (i = 0; i < length; ++i) - { - u_int32_t temp = (crc ^ ((u_int32_t) buffer[i])) & 0xFF; - crc = (crc >> 8) ^ g_crc_table[temp]; - } - - return crc; -} - -/* - * get a random block of data per fips 186-2 - */ -void -random_block(Block b, int addOptional) -{ - SHA1_CTX sha1_ctx; - - int repeatCount = 0; - do - { - // do one iteration - - if (addOptional) - { - // create an xSeed to add. - Block xSeed; - prngOutput (gPrngRef, (BYTE*) &xSeed, sizeof (xSeed)); - - // add the seed to the previous value of g_xkey - add_blocks (g_xkey, xSeed, 0); - } - - // initialize the value of H - FIPS_SHA1Init(&sha1_ctx); - - // to stay compatible with the FIPS specification, we need to flip the bytes in - // g_xkey to little endian byte order. In our case, this makes exactly no difference - // (random is random), but we need to do it anyway to keep FIPS happy - - // compute "G" - FIPS_SHA1Update(&sha1_ctx, g_xkey, kBlockSize); - - // add zeros to fill the internal SHA-1 buffer - FIPS_SHA1Update (&sha1_ctx, (const u_int8_t *)zeros, sizeof (zeros)); - - // we have to do a byte order correction here because the sha1 math is being done internally - // as u_int32_t, not a stream of bytes. Since we maintain our data as a byte stream, we need - // to convert - - u_int32_t* finger = (u_int32_t*) b; - - unsigned j; - for (j = 0; j < kBlockSize / sizeof (u_int32_t); ++j) - { - *finger++ = OSSwapHostToBigInt32(sha1_ctx.h.b32[j]); - } - - // calculate the CRC-32 of the block - u_int32_t new_crc = CalculateCRC(sha1_ctx.h.b8, sizeof (Block)); - - // make sure we don't repeat - int cmp = new_crc == gLastBlockChecksum; - gLastBlockChecksum = new_crc; - if (!g_SelfTestInitialized) - { - g_SelfTestInitialized = 1; - return; - } - else if (!cmp) - { - return; - } - - repeatCount += 1; - - // fix up the next value of g_xkey - add_blocks (g_xkey, b, 1); - } while (repeatCount < 2); - - /* - * If we got here, three sucessive checksums of the random number - * generator have been the same. Since the odds of this happening are - * 1 in 18,446,744,073,709,551,616, (1 in 18 quintillion) one of the following has - * most likely happened: - * - * 1: There is a significant bug in this code. - * 2: There has been a massive system failure. - * 3: The universe has ceased to exist. - * - * There is no good way to recover from any of these cases. We - * therefore panic. - */ - - panic("FIPS random self-test failed."); -} - -/* - *Initialize ONLY the Yarrow generator. - */ -void -PreliminarySetup(void) -{ - prng_error_status perr; - - /* create a Yarrow object */ - perr = prngInitialize(&gPrngRef); - if (perr != 0) { - printf ("Couldn't initialize Yarrow, /dev/random will not work.\n"); - return; - } - - /* clear the error flag, reads and write should then work */ - gRandomError = 0; - - struct timeval tt; - char buffer [16]; - - /* get a little non-deterministic data as an initial seed. */ - microtime(&tt); - - /* - * So how much of the system clock is entropic? - * It's hard to say, but assume that at least the - * least significant byte of a 64 bit structure - * is entropic. It's probably more, how can you figure - * the exact time the user turned the computer on, for example. - */ - perr = prngInput(gPrngRef, (BYTE*) &tt, sizeof (tt), SYSTEM_SOURCE, 8); - if (perr != 0) { - /* an error, complain */ - printf ("Couldn't seed Yarrow.\n"); - return; - } - - /* turn the data around */ - perr = prngOutput(gPrngRef, (BYTE*) buffer, sizeof (buffer)); - - /* and scramble it some more */ - perr = prngForceReseed(gPrngRef, RESEED_TICKS); - - /* make a mutex to control access */ - gYarrowGrpAttr = lck_grp_attr_alloc_init(); - gYarrowGrp = lck_grp_alloc_init("random", gYarrowGrpAttr); - gYarrowAttr = lck_attr_alloc_init(); - gYarrowMutex = lck_mtx_alloc_init(gYarrowGrp, gYarrowAttr); - - fips_initialize (); -} - -const Block kKnownAnswer = {0x92, 0xb4, 0x04, 0xe5, 0x56, 0x58, 0x8c, 0xed, 0x6c, 0x1a, 0xcd, 0x4e, 0xbf, 0x05, 0x3f, 0x68, 0x09, 0xf7, 0x3a, 0x93}; - -void -fips_initialize(void) -{ - /* So that we can do the self test, set the seed to zero */ - memset(&g_xkey, 0, sizeof(g_xkey)); - - /* other initializations */ - memset (zeros, 0, sizeof (zeros)); - g_bytes_used = 0; - random_block(g_random_data, FALSE); - - // check here to see if we got the initial data we were expecting - if (memcmp(kKnownAnswer, g_random_data, kBlockSize) != 0) - { - panic("FIPS random self test failed"); - } - - // now do the random block again to make sure that userland doesn't get predicatable data - random_block(g_random_data, TRUE); -} /* * Called to initialize our device, @@ -384,36 +88,25 @@ random_init(void) { int ret; - if (gRandomInstalled) - return; - - /* install us in the file system */ - gRandomInstalled = 1; - - /* setup yarrow and the mutex */ - PreliminarySetup(); - ret = cdevsw_add(RANDOM_MAJOR, &random_cdevsw); if (ret < 0) { - printf("random_init: failed to allocate a major number!\n"); - gRandomInstalled = 0; - return; + panic("random_init: failed to allocate a major number!"); } - devfs_make_node(makedev (ret, 0), DEVFS_CHAR, - UID_ROOT, GID_WHEEL, 0666, "random", 0); + devfs_make_node(makedev(ret, RANDOM_MINOR), DEVFS_CHAR, + UID_ROOT, GID_WHEEL, 0666, "random", 0); /* - * also make urandom + * also make urandom * (which is exactly the same thing in our context) */ - devfs_make_node(makedev (ret, 1), DEVFS_CHAR, - UID_ROOT, GID_WHEEL, 0666, "urandom", 0); + devfs_make_node(makedev(ret, URANDOM_MINOR), DEVFS_CHAR, + UID_ROOT, GID_WHEEL, 0666, "urandom", 0); } int -random_ioctl( __unused dev_t dev, u_long cmd, __unused caddr_t data, - __unused int flag, __unused struct proc *p ) +random_ioctl( __unused dev_t dev, u_long cmd, __unused caddr_t data, + __unused int flag, __unused struct proc *p ) { switch (cmd) { case FIONBIO: @@ -423,47 +116,44 @@ random_ioctl( __unused dev_t dev, u_long cmd, __unused caddr_t data, return ENODEV; } - return (0); + return 0; } /* * Open the device. Make sure init happened, and make sure the caller is * authorized. */ - + int random_open(__unused dev_t dev, int flags, __unused int devtype, __unused struct proc *p) { - if (gRandomError != 0) { - /* forget it, yarrow didn't come up */ - return (ENOTSUP); - } - /* * if we are being opened for write, * make sure that we have privledges do so */ if (flags & FWRITE) { - if (securelevel >= 2) - return (EPERM); + if (securelevel >= 2) { + return EPERM; + } #ifndef __APPLE__ - if ((securelevel >= 1) && proc_suser(p)) - return (EPERM); -#endif /* !__APPLE__ */ + if ((securelevel >= 1) && proc_suser(p)) { + return EPERM; + } +#endif /* !__APPLE__ */ } - return (0); + return 0; } /* * close the device. */ - + int random_close(__unused dev_t dev, __unused int flags, __unused int mode, __unused struct proc *p) { - return (0); + return 0; } @@ -472,123 +162,58 @@ random_close(__unused dev_t dev, __unused int flags, __unused int mode, __unused * prng. */ int -random_write (__unused dev_t dev, struct uio *uio, __unused int ioflag) +random_write(dev_t dev, struct uio *uio, __unused int ioflag) { - int retCode = 0; - char rdBuffer[256]; - - if (gRandomError != 0) { - return (ENOTSUP); - } - - /* get control of the Yarrow instance, Yarrow is NOT thread safe */ - lck_mtx_lock(gYarrowMutex); - - /* Security server is sending us entropy */ - - while (uio_resid(uio) > 0 && retCode == 0) { - /* get the user's data */ - int bytesToInput = min(uio_resid(uio), sizeof (rdBuffer)); - retCode = uiomove(rdBuffer, bytesToInput, uio); - if (retCode != 0) - goto /*ugh*/ error_exit; - - /* put it in Yarrow */ - if (prngInput(gPrngRef, (BYTE*) rdBuffer, - bytesToInput, SYSTEM_SOURCE, - bytesToInput * 8) != 0) { - retCode = EIO; - goto error_exit; - } - } - - /* force a reseed */ - if (prngForceReseed(gPrngRef, RESEED_TICKS) != 0) { - retCode = EIO; - goto error_exit; - } - - /* retCode should be 0 at this point */ - -error_exit: /* do this to make sure the mutex unlocks. */ - lck_mtx_unlock(gYarrowMutex); - return (retCode); + int retCode = 0; + char rdBuffer[256]; + + if (minor(dev) != RANDOM_MINOR) { + return EPERM; + } + + /* Security server is sending us entropy */ + + while (uio_resid(uio) > 0 && retCode == 0) { + /* get the user's data */ + int bytesToInput = MIN(uio_resid(uio), + (user_ssize_t) sizeof(rdBuffer)); + retCode = uiomove(rdBuffer, bytesToInput, uio); + if (retCode != 0) { + break; + } + retCode = write_random(rdBuffer, bytesToInput); + if (retCode != 0) { + break; + } + } + + return retCode; } /* * return data to the caller. Results unpredictable. - */ + */ int random_read(__unused dev_t dev, struct uio *uio, __unused int ioflag) { - int retCode = 0; - - if (gRandomError != 0) - return (ENOTSUP); - - /* lock down the mutex */ - lck_mtx_lock(gYarrowMutex); - - - int bytes_remaining = uio_resid(uio); - while (bytes_remaining > 0 && retCode == 0) { - /* get the user's data */ - int bytes_to_read = 0; - - int bytes_available = kBlockSize - g_bytes_used; - if (bytes_available == 0) - { - random_block(g_random_data, TRUE); - g_bytes_used = 0; - bytes_available = kBlockSize; + int retCode = 0; + char buffer[512]; + + user_ssize_t bytes_remaining = uio_resid(uio); + while (bytes_remaining > 0 && retCode == 0) { + int bytesToRead = MIN(bytes_remaining, + (user_ssize_t) sizeof(buffer)); + read_random(buffer, bytesToRead); + + retCode = uiomove(buffer, bytesToRead, uio); + if (retCode != 0) { + break; } - - bytes_to_read = min (bytes_remaining, bytes_available); - - retCode = uiomove(((caddr_t)g_random_data)+ g_bytes_used, bytes_to_read, uio); - g_bytes_used += bytes_to_read; - - if (retCode != 0) - goto error_exit; - + bytes_remaining = uio_resid(uio); - } - - retCode = 0; - -error_exit: - lck_mtx_unlock(gYarrowMutex); - return retCode; -} + } -/* export good random numbers to the rest of the kernel */ -void -read_random(void* buffer, u_int numbytes) -{ - if (gYarrowMutex == 0) { /* are we initialized? */ - PreliminarySetup (); - } - - lck_mtx_lock(gYarrowMutex); - int bytes_read = 0; - - int bytes_remaining = numbytes; - while (bytes_remaining > 0) { - int bytes_to_read = min(bytes_remaining, kBlockSize - g_bytes_used); - if (bytes_to_read == 0) - { - random_block(g_random_data, TRUE); - g_bytes_used = 0; - bytes_to_read = min(bytes_remaining, kBlockSize); - } - - memmove ((u_int8_t*) buffer + bytes_read, ((u_int8_t*)g_random_data)+ g_bytes_used, bytes_to_read); - g_bytes_used += bytes_to_read; - bytes_read += bytes_to_read; - bytes_remaining -= bytes_to_read; - } - - lck_mtx_unlock(gYarrowMutex); + return retCode; } /* @@ -598,7 +223,26 @@ u_int32_t RandomULong(void) { u_int32_t buf; - read_random(&buf, sizeof (buf)); - return (buf); + read_random(&buf, sizeof(buf)); + return buf; } + +int +getentropy(__unused struct proc * p, struct getentropy_args *gap, __unused int * ret) +{ + user_addr_t user_addr; + uint32_t user_size; + char buffer[256]; + + user_addr = (vm_map_offset_t)gap->buffer; + user_size = gap->size; + /* Can't request more than 256 random bytes + * at once. Complying with openbsd getentropy() + */ + if (user_size > sizeof(buffer)) { + return EINVAL; + } + read_random(buffer, user_size); + return copyout(buffer, user_addr, user_size); +}