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Diffstat (limited to 'security/nss/lib/util/secport.c')
| -rw-r--r-- | security/nss/lib/util/secport.c | 879 |
1 files changed, 879 insertions, 0 deletions
diff --git a/security/nss/lib/util/secport.c b/security/nss/lib/util/secport.c new file mode 100644 index 0000000000..fb5223d64a --- /dev/null +++ b/security/nss/lib/util/secport.c @@ -0,0 +1,879 @@ +/* This Source Code Form is subject to the terms of the Mozilla Public + * License, v. 2.0. If a copy of the MPL was not distributed with this + * file, You can obtain one at http://mozilla.org/MPL/2.0/. */ + +/* + * secport.c - portability interfaces for security libraries + * + * This file abstracts out libc functionality that libsec depends on + * + * NOTE - These are not public interfaces + */ + +#include "seccomon.h" +#include "prmem.h" +#include "prerror.h" +#include "plarena.h" +#include "secerr.h" +#include "prmon.h" +#include "nssilock.h" +#include "secport.h" +#include "prenv.h" +#include "prinit.h" + +#include <stdint.h> + +#ifdef DEBUG +#define THREADMARK +#endif /* DEBUG */ + +#ifdef THREADMARK +#include "prthread.h" +#endif /* THREADMARK */ + +#if defined(XP_UNIX) || defined(XP_OS2) +#include <stdlib.h> +#else +#include "wtypes.h" +#endif + +#define SET_ERROR_CODE /* place holder for code to set PR error code. */ + +#ifdef THREADMARK +typedef struct threadmark_mark_str { + struct threadmark_mark_str *next; + void *mark; +} threadmark_mark; + +#endif /* THREADMARK */ + +/* The value of this magic must change each time PORTArenaPool changes. */ +#define ARENAPOOL_MAGIC 0xB8AC9BDF + +#define CHEAP_ARENAPOOL_MAGIC 0x3F16BB09 + +typedef struct PORTArenaPool_str { + PLArenaPool arena; + PRUint32 magic; + PRLock *lock; +#ifdef THREADMARK + PRThread *marking_thread; + threadmark_mark *first_mark; +#endif +} PORTArenaPool; + +/* locations for registering Unicode conversion functions. + * XXX is this the appropriate location? or should they be + * moved to client/server specific locations? + */ +PORTCharConversionFunc ucs4Utf8ConvertFunc; +PORTCharConversionFunc ucs2Utf8ConvertFunc; +PORTCharConversionWSwapFunc ucs2AsciiConvertFunc; + +/* NSPR memory allocation functions (PR_Malloc, PR_Calloc, and PR_Realloc) + * use the PRUint32 type for the size parameter. Before we pass a size_t or + * unsigned long size to these functions, we need to ensure it is <= half of + * the maximum PRUint32 value to avoid truncation and catch a negative size. + */ +#define MAX_SIZE (PR_UINT32_MAX >> 1) + +void * +PORT_Alloc(size_t bytes) +{ + void *rv = NULL; + + if (bytes <= MAX_SIZE) { + /* Always allocate a non-zero amount of bytes */ + rv = PR_Malloc(bytes ? bytes : 1); + } + if (!rv) { + PORT_SetError(SEC_ERROR_NO_MEMORY); + } + return rv; +} + +void * +PORT_Realloc(void *oldptr, size_t bytes) +{ + void *rv = NULL; + + if (bytes <= MAX_SIZE) { + rv = PR_Realloc(oldptr, bytes); + } + if (!rv) { + PORT_SetError(SEC_ERROR_NO_MEMORY); + } + return rv; +} + +void * +PORT_ZAlloc(size_t bytes) +{ + void *rv = NULL; + + if (bytes <= MAX_SIZE) { + /* Always allocate a non-zero amount of bytes */ + rv = PR_Calloc(1, bytes ? bytes : 1); + } + if (!rv) { + PORT_SetError(SEC_ERROR_NO_MEMORY); + } + return rv; +} + +/* aligned_alloc is C11. This is an alternative to get aligned memory. */ +void * +PORT_ZAllocAligned(size_t bytes, size_t alignment, void **mem) +{ + size_t x = alignment - 1; + + /* This only works if alignment is a power of 2. */ + if ((alignment == 0) || (alignment & (alignment - 1))) { + PORT_SetError(SEC_ERROR_INVALID_ARGS); + return NULL; + } + + if (!mem) { + return NULL; + } + + /* Always allocate a non-zero amount of bytes */ + *mem = PORT_ZAlloc((bytes ? bytes : 1) + x); + if (!*mem) { + PORT_SetError(SEC_ERROR_NO_MEMORY); + return NULL; + } + + return (void *)(((uintptr_t)*mem + x) & ~(uintptr_t)x); +} + +void * +PORT_ZAllocAlignedOffset(size_t size, size_t alignment, size_t offset) +{ + PORT_Assert(offset < size); + if (offset > size) { + return NULL; + } + + void *mem = NULL; + void *v = PORT_ZAllocAligned(size, alignment, &mem); + if (!v) { + return NULL; + } + + PORT_Assert(mem); + *((void **)((uintptr_t)v + offset)) = mem; + return v; +} + +void +PORT_Free(void *ptr) +{ + if (ptr) { + PR_Free(ptr); + } +} + +void +PORT_ZFree(void *ptr, size_t len) +{ + if (ptr) { + memset(ptr, 0, len); + PR_Free(ptr); + } +} + +char * +PORT_Strdup(const char *str) +{ + size_t len = PORT_Strlen(str) + 1; + char *newstr; + + newstr = (char *)PORT_Alloc(len); + if (newstr) { + PORT_Memcpy(newstr, str, len); + } + return newstr; +} + +void +PORT_SetError(int value) +{ + PR_SetError(value, 0); + return; +} + +int +PORT_GetError(void) +{ + return (PR_GetError()); +} + +/********************* Arena code follows ***************************** + * ArenaPools are like heaps. The memory in them consists of large blocks, + * called arenas, which are allocated from the/a system heap. Inside an + * ArenaPool, the arenas are organized as if they were in a stack. Newly + * allocated arenas are "pushed" on that stack. When you attempt to + * allocate memory from an ArenaPool, the code first looks to see if there + * is enough unused space in the top arena on the stack to satisfy your + * request, and if so, your request is satisfied from that arena. + * Otherwise, a new arena is allocated (or taken from NSPR's list of freed + * arenas) and pushed on to the stack. The new arena is always big enough + * to satisfy the request, and is also at least a minimum size that is + * established at the time that the ArenaPool is created. + * + * The ArenaMark function returns the address of a marker in the arena at + * the top of the arena stack. It is the address of the place in the arena + * on the top of the arena stack from which the next block of memory will + * be allocated. Each ArenaPool has its own separate stack, and hence + * marks are only relevant to the ArenaPool from which they are gotten. + * Marks may be nested. That is, a thread can get a mark, and then get + * another mark. + * + * It is intended that all the marks in an ArenaPool may only be owned by a + * single thread. In DEBUG builds, this is enforced. In non-DEBUG builds, + * it is not. In DEBUG builds, when a thread gets a mark from an + * ArenaPool, no other thread may acquire a mark in that ArenaPool while + * that mark exists, that is, until that mark is unmarked or released. + * Therefore, it is important that every mark be unmarked or released when + * the creating thread has no further need for exclusive ownership of the + * right to manage the ArenaPool. + * + * The ArenaUnmark function discards the ArenaMark at the address given, + * and all marks nested inside that mark (that is, acquired from that same + * ArenaPool while that mark existed). It is an error for a thread other + * than the mark's creator to try to unmark it. When a thread has unmarked + * all its marks from an ArenaPool, then another thread is able to set + * marks in that ArenaPool. ArenaUnmark does not deallocate (or "pop") any + * memory allocated from the ArenaPool since the mark was created. + * + * ArenaRelease "pops" the stack back to the mark, deallocating all the + * memory allocated from the arenas in the ArenaPool since that mark was + * created, and removing any arenas from the ArenaPool that have no + * remaining active allocations when that is done. It implicitly releases + * any marks nested inside the mark being explicitly released. It is the + * only operation, other than destroying the arenapool, that potentially + * reduces the number of arenas on the stack. Otherwise, the stack grows + * until the arenapool is destroyed, at which point all the arenas are + * freed or returned to a "free arena list", depending on their sizes. + */ +PLArenaPool * +PORT_NewArena(unsigned long chunksize) +{ + PORTArenaPool *pool; + + if (chunksize > MAX_SIZE) { + PORT_SetError(SEC_ERROR_NO_MEMORY); + return NULL; + } + pool = PORT_ZNew(PORTArenaPool); + if (!pool) { + return NULL; + } + pool->magic = ARENAPOOL_MAGIC; + pool->lock = PZ_NewLock(nssILockArena); + if (!pool->lock) { + PORT_Free(pool); + return NULL; + } + PL_InitArenaPool(&pool->arena, "security", chunksize, sizeof(double)); + return (&pool->arena); +} + +void +PORT_InitCheapArena(PORTCheapArenaPool *pool, unsigned long chunksize) +{ + pool->magic = CHEAP_ARENAPOOL_MAGIC; + PL_InitArenaPool(&pool->arena, "security", chunksize, sizeof(double)); +} + +void * +PORT_ArenaAlloc(PLArenaPool *arena, size_t size) +{ + void *p = NULL; + + PORTArenaPool *pool = (PORTArenaPool *)arena; + + if (size <= 0) { + size = 1; + } + + if (size > MAX_SIZE) { + /* you lose. */ + } else + /* Is it one of ours? Assume so and check the magic */ + if (ARENAPOOL_MAGIC == pool->magic) { + PZ_Lock(pool->lock); +#ifdef THREADMARK + /* Most likely one of ours. Is there a thread id? */ + if (pool->marking_thread && + pool->marking_thread != PR_GetCurrentThread()) { + /* Another thread holds a mark in this arena */ + PZ_Unlock(pool->lock); + PORT_SetError(SEC_ERROR_NO_MEMORY); + PORT_Assert(0); + return NULL; + } /* tid != null */ +#endif /* THREADMARK */ + PL_ARENA_ALLOCATE(p, arena, size); + PZ_Unlock(pool->lock); + } else { + PL_ARENA_ALLOCATE(p, arena, size); + } + + if (!p) { + PORT_SetError(SEC_ERROR_NO_MEMORY); + } + + return (p); +} + +void * +PORT_ArenaZAlloc(PLArenaPool *arena, size_t size) +{ + void *p; + + if (size <= 0) + size = 1; + + p = PORT_ArenaAlloc(arena, size); + + if (p) { + PORT_Memset(p, 0, size); + } + + return (p); +} + +static PRCallOnceType setupUseFreeListOnce; +static PRBool useFreeList; + +static PRStatus +SetupUseFreeList(void) +{ + useFreeList = (PR_GetEnvSecure("NSS_DISABLE_ARENA_FREE_LIST") == NULL); + return PR_SUCCESS; +} + +/* + * If zero is true, zeroize the arena memory before freeing it. + */ +void +PORT_FreeArena(PLArenaPool *arena, PRBool zero) +{ + PORTArenaPool *pool = (PORTArenaPool *)arena; + PRLock *lock = (PRLock *)0; + size_t len = sizeof *arena; + + if (!pool) + return; + if (ARENAPOOL_MAGIC == pool->magic) { + len = sizeof *pool; + lock = pool->lock; + PZ_Lock(lock); + } + if (zero) { + PL_ClearArenaPool(arena, 0); + } + (void)PR_CallOnce(&setupUseFreeListOnce, &SetupUseFreeList); + if (useFreeList) { + PL_FreeArenaPool(arena); + } else { + PL_FinishArenaPool(arena); + } + PORT_ZFree(arena, len); + if (lock) { + PZ_Unlock(lock); + PZ_DestroyLock(lock); + } +} + +void +PORT_DestroyCheapArena(PORTCheapArenaPool *pool) +{ + (void)PR_CallOnce(&setupUseFreeListOnce, &SetupUseFreeList); + if (useFreeList) { + PL_FreeArenaPool(&pool->arena); + } else { + PL_FinishArenaPool(&pool->arena); + } +} + +void * +PORT_ArenaGrow(PLArenaPool *arena, void *ptr, size_t oldsize, size_t newsize) +{ + PORTArenaPool *pool = (PORTArenaPool *)arena; + PORT_Assert(newsize >= oldsize); + + if (newsize > MAX_SIZE) { + PORT_SetError(SEC_ERROR_NO_MEMORY); + return NULL; + } + + if (ARENAPOOL_MAGIC == pool->magic) { + PZ_Lock(pool->lock); + /* Do we do a THREADMARK check here? */ + PL_ARENA_GROW(ptr, arena, oldsize, (newsize - oldsize)); + PZ_Unlock(pool->lock); + } else { + PL_ARENA_GROW(ptr, arena, oldsize, (newsize - oldsize)); + } + + return (ptr); +} + +void * +PORT_ArenaMark(PLArenaPool *arena) +{ + void *result; + + PORTArenaPool *pool = (PORTArenaPool *)arena; + if (ARENAPOOL_MAGIC == pool->magic) { + PZ_Lock(pool->lock); +#ifdef THREADMARK + { + threadmark_mark *tm, **pw; + PRThread *currentThread = PR_GetCurrentThread(); + + if (!pool->marking_thread) { + /* First mark */ + pool->marking_thread = currentThread; + } else if (currentThread != pool->marking_thread) { + PZ_Unlock(pool->lock); + PORT_SetError(SEC_ERROR_NO_MEMORY); + PORT_Assert(0); + return NULL; + } + + result = PL_ARENA_MARK(arena); + PL_ARENA_ALLOCATE(tm, arena, sizeof(threadmark_mark)); + if (!tm) { + PZ_Unlock(pool->lock); + PORT_SetError(SEC_ERROR_NO_MEMORY); + return NULL; + } + + tm->mark = result; + tm->next = (threadmark_mark *)NULL; + + pw = &pool->first_mark; + while (*pw) { + pw = &(*pw)->next; + } + + *pw = tm; + } +#else /* THREADMARK */ + result = PL_ARENA_MARK(arena); +#endif /* THREADMARK */ + PZ_Unlock(pool->lock); + } else { + /* a "pure" NSPR arena */ + result = PL_ARENA_MARK(arena); + } + return result; +} + +/* + * This function accesses the internals of PLArena, which is why it needs + * to use the NSPR internal macro PL_MAKE_MEM_UNDEFINED before the memset + * calls. + * + * We should move this function to NSPR as PL_ClearArenaAfterMark or add + * a PL_ARENA_CLEAR_AND_RELEASE macro. + * + * TODO: remove the #ifdef PL_MAKE_MEM_UNDEFINED tests when NSPR 4.10+ is + * widely available. + */ +static void +port_ArenaZeroAfterMark(PLArenaPool *arena, void *mark) +{ + PLArena *a = arena->current; + if (a->base <= (PRUword)mark && (PRUword)mark <= a->avail) { +/* fast path: mark falls in the current arena */ +#ifdef PL_MAKE_MEM_UNDEFINED + PL_MAKE_MEM_UNDEFINED(mark, a->avail - (PRUword)mark); +#endif + memset(mark, 0, a->avail - (PRUword)mark); + } else { + /* slow path: need to find the arena that mark falls in */ + for (a = arena->first.next; a; a = a->next) { + PR_ASSERT(a->base <= a->avail && a->avail <= a->limit); + if (a->base <= (PRUword)mark && (PRUword)mark <= a->avail) { +#ifdef PL_MAKE_MEM_UNDEFINED + PL_MAKE_MEM_UNDEFINED(mark, a->avail - (PRUword)mark); +#endif + memset(mark, 0, a->avail - (PRUword)mark); + a = a->next; + break; + } + } + for (; a; a = a->next) { + PR_ASSERT(a->base <= a->avail && a->avail <= a->limit); +#ifdef PL_MAKE_MEM_UNDEFINED + PL_MAKE_MEM_UNDEFINED((void *)a->base, a->avail - a->base); +#endif + memset((void *)a->base, 0, a->avail - a->base); + } + } +} + +static void +port_ArenaRelease(PLArenaPool *arena, void *mark, PRBool zero) +{ + PORTArenaPool *pool = (PORTArenaPool *)arena; + if (ARENAPOOL_MAGIC == pool->magic) { + PZ_Lock(pool->lock); +#ifdef THREADMARK + { + threadmark_mark **pw; + + if (PR_GetCurrentThread() != pool->marking_thread) { + PZ_Unlock(pool->lock); + PORT_SetError(SEC_ERROR_NO_MEMORY); + PORT_Assert(0); + return /* no error indication available */; + } + + pw = &pool->first_mark; + while (*pw && (mark != (*pw)->mark)) { + pw = &(*pw)->next; + } + + if (!*pw) { + /* bad mark */ + PZ_Unlock(pool->lock); + PORT_SetError(SEC_ERROR_NO_MEMORY); + PORT_Assert(0); + return /* no error indication available */; + } + + *pw = (threadmark_mark *)NULL; + + if (zero) { + port_ArenaZeroAfterMark(arena, mark); + } + PL_ARENA_RELEASE(arena, mark); + + if (!pool->first_mark) { + pool->marking_thread = (PRThread *)NULL; + } + } +#else /* THREADMARK */ + if (zero) { + port_ArenaZeroAfterMark(arena, mark); + } + PL_ARENA_RELEASE(arena, mark); +#endif /* THREADMARK */ + PZ_Unlock(pool->lock); + } else { + if (zero) { + port_ArenaZeroAfterMark(arena, mark); + } + PL_ARENA_RELEASE(arena, mark); + } +} + +void +PORT_ArenaRelease(PLArenaPool *arena, void *mark) +{ + port_ArenaRelease(arena, mark, PR_FALSE); +} + +/* + * Zeroize the arena memory before releasing it. + */ +void +PORT_ArenaZRelease(PLArenaPool *arena, void *mark) +{ + port_ArenaRelease(arena, mark, PR_TRUE); +} + +void +PORT_ArenaUnmark(PLArenaPool *arena, void *mark) +{ +#ifdef THREADMARK + PORTArenaPool *pool = (PORTArenaPool *)arena; + if (ARENAPOOL_MAGIC == pool->magic) { + threadmark_mark **pw; + + PZ_Lock(pool->lock); + + if (PR_GetCurrentThread() != pool->marking_thread) { + PZ_Unlock(pool->lock); + PORT_SetError(SEC_ERROR_NO_MEMORY); + PORT_Assert(0); + return /* no error indication available */; + } + + pw = &pool->first_mark; + while (((threadmark_mark *)NULL != *pw) && (mark != (*pw)->mark)) { + pw = &(*pw)->next; + } + + if ((threadmark_mark *)NULL == *pw) { + /* bad mark */ + PZ_Unlock(pool->lock); + PORT_SetError(SEC_ERROR_NO_MEMORY); + PORT_Assert(0); + return /* no error indication available */; + } + + *pw = (threadmark_mark *)NULL; + + if (!pool->first_mark) { + pool->marking_thread = (PRThread *)NULL; + } + + PZ_Unlock(pool->lock); + } +#endif /* THREADMARK */ +} + +char * +PORT_ArenaStrdup(PLArenaPool *arena, const char *str) +{ + int len = PORT_Strlen(str) + 1; + char *newstr; + + newstr = (char *)PORT_ArenaAlloc(arena, len); + if (newstr) { + PORT_Memcpy(newstr, str, len); + } + return newstr; +} + +/********************** end of arena functions ***********************/ + +/****************** unicode conversion functions ***********************/ +/* + * NOTE: These conversion functions all assume that the multibyte + * characters are going to be in NETWORK BYTE ORDER, not host byte + * order. This is because the only time we deal with UCS-2 and UCS-4 + * are when the data was received from or is going to be sent out + * over the wire (in, e.g. certificates). + */ + +void +PORT_SetUCS4_UTF8ConversionFunction(PORTCharConversionFunc convFunc) +{ + ucs4Utf8ConvertFunc = convFunc; +} + +void +PORT_SetUCS2_ASCIIConversionFunction(PORTCharConversionWSwapFunc convFunc) +{ + ucs2AsciiConvertFunc = convFunc; +} + +void +PORT_SetUCS2_UTF8ConversionFunction(PORTCharConversionFunc convFunc) +{ + ucs2Utf8ConvertFunc = convFunc; +} + +PRBool +PORT_UCS4_UTF8Conversion(PRBool toUnicode, unsigned char *inBuf, + unsigned int inBufLen, unsigned char *outBuf, + unsigned int maxOutBufLen, unsigned int *outBufLen) +{ + if (!ucs4Utf8ConvertFunc) { + return sec_port_ucs4_utf8_conversion_function(toUnicode, + inBuf, inBufLen, outBuf, maxOutBufLen, outBufLen); + } + + return (*ucs4Utf8ConvertFunc)(toUnicode, inBuf, inBufLen, outBuf, + maxOutBufLen, outBufLen); +} + +PRBool +PORT_UCS2_UTF8Conversion(PRBool toUnicode, unsigned char *inBuf, + unsigned int inBufLen, unsigned char *outBuf, + unsigned int maxOutBufLen, unsigned int *outBufLen) +{ + if (!ucs2Utf8ConvertFunc) { + return sec_port_ucs2_utf8_conversion_function(toUnicode, + inBuf, inBufLen, outBuf, maxOutBufLen, outBufLen); + } + + return (*ucs2Utf8ConvertFunc)(toUnicode, inBuf, inBufLen, outBuf, + maxOutBufLen, outBufLen); +} + +PRBool +PORT_ISO88591_UTF8Conversion(const unsigned char *inBuf, + unsigned int inBufLen, unsigned char *outBuf, + unsigned int maxOutBufLen, unsigned int *outBufLen) +{ + return sec_port_iso88591_utf8_conversion_function(inBuf, inBufLen, + outBuf, maxOutBufLen, outBufLen); +} + +PRBool +PORT_UCS2_ASCIIConversion(PRBool toUnicode, unsigned char *inBuf, + unsigned int inBufLen, unsigned char *outBuf, + unsigned int maxOutBufLen, unsigned int *outBufLen, + PRBool swapBytes) +{ + if (!ucs2AsciiConvertFunc) { + return PR_FALSE; + } + + return (*ucs2AsciiConvertFunc)(toUnicode, inBuf, inBufLen, outBuf, + maxOutBufLen, outBufLen, swapBytes); +} + +/* Portable putenv. Creates/replaces an environment variable of the form + * envVarName=envValue + */ +int +NSS_PutEnv(const char *envVarName, const char *envValue) +{ + SECStatus result = SECSuccess; +#ifdef _WIN32 + PRBool setOK; + + setOK = SetEnvironmentVariable(envVarName, envValue); + if (!setOK) { + SET_ERROR_CODE + return SECFailure; + } +#elif defined(__GNUC__) && __GNUC__ >= 7 + int setEnvFailed; + setEnvFailed = setenv(envVarName, envValue, 1); + if (setEnvFailed) { + SET_ERROR_CODE + return SECFailure; + } +#else + char *encoded = (char *)PORT_ZAlloc(strlen(envVarName) + 2 + strlen(envValue)); + if (!encoded) { + return SECFailure; + } + strcpy(encoded, envVarName); + strcat(encoded, "="); + strcat(encoded, envValue); + int putEnvFailed = putenv(encoded); /* adopt. */ + + if (putEnvFailed) { + SET_ERROR_CODE + result = SECFailure; + PORT_Free(encoded); + } +#endif + return result; +} + +/* + * Perform a constant-time compare of two memory regions. The return value is + * 0 if the memory regions are equal and non-zero otherwise. + */ +int +NSS_SecureMemcmp(const void *ia, const void *ib, size_t n) +{ + const unsigned char *a = (const unsigned char *)ia; + const unsigned char *b = (const unsigned char *)ib; + int r = 0; + + for (size_t i = 0; i < n; ++i) { + r |= a[i] ^ b[i]; + } + + /* 0 <= r < 256, so -r has bit 8 set when r != 0 */ + return 1 & (-r >> 8); +} + +/* + * Perform a constant-time check if a memory region is all 0. The return value + * is 0 if the memory region is all zero. + */ +unsigned int +NSS_SecureMemcmpZero(const void *mem, size_t n) +{ + const unsigned char *a = (const unsigned char *)mem; + int r = 0; + + for (size_t i = 0; i < n; ++i) { + r |= a[i]; + } + + /* 0 <= r < 256, so -r has bit 8 set when r != 0 */ + return 1 & (-r >> 8); +} + +/* + * A "value barrier" prevents the compiler from making optimizations based on + * the value that a variable takes. + * + * Standard C does not have value barriers, so C implementations of them are + * compiler-specific and are not guaranteed to be effective. Thus, the value + * barriers here are a best-effort, defense-in-depth, strategy. They are not a + * substitute for standard constant-time programming discipline. + * + * Some implementations have a performance penalty, so value barriers should + * be used sparingly. + */ +static inline int +value_barrier_int(int x) +{ +#if defined(__GNUC__) || defined(__clang__) + /* This inline assembly trick from Chandler Carruth's CppCon 2015 talk + * generates no instructions. + * + * "+r"(x) means that x will be mapped to a register that is both an input + * and an output to the assembly routine (""). The compiler will not + * inspect the assembly routine itself, so it cannot assume anything about + * the value of x after this line. + */ + __asm__("" + : "+r"(x) + : /* no other inputs */); + return x; +#else + /* If the compiler does not support the inline assembly trick above, we can + * put x in `volatile` storage and read it out again. This will generate + * explict store and load instructions, and possibly more depending on the + * target. + */ + volatile int y = x; + return y; +#endif +} + +/* + * A branch-free implementation of + * if (!b) { + * memmove(dest, src0, n); + * } else { + * memmove(dest, src1, n); + * } + * + * The memmove is performed with src0 if `b == 0` and with src1 + * otherwise. + * + * As with memmove, the selected src can overlap dest. + * + * Each of dest, src0, and src1 must point to an allocated buffer + * of at least n bytes. + */ +void +NSS_SecureSelect(void *dest, const void *src0, const void *src1, size_t n, unsigned char b) + +{ + // This value barrier makes it safe for the compiler to inline + // NSS_SecureSelect into a routine where it could otherwise infer something + // about the value of b, e.g. that b is 0/1 valued. + int w = value_barrier_int(b); + + // 0 <= b < 256, and int is at least 16 bits, so -w has bits 8-15 + // set when w != 0. + unsigned char mask = 0xff & (-w >> 8); + + for (size_t i = 0; i < n; ++i) { + unsigned char s0i = ((unsigned char *)src0)[i]; + unsigned char s1i = ((unsigned char *)src1)[i]; + // if mask == 0 this simplifies to s0 ^ 0 + // if mask == -1 this simplifies to s0 ^ s0 ^ s1 + ((unsigned char *)dest)[i] = s0i ^ (mask & (s0i ^ s1i)); + } +} |