cuberite/libdeflate
1
0
Fork 0
mirror of https://github.com/cuberite/libdeflate.git synced 2025-09-07 19:26:29 -04:00
Code Issues Packages Projects Releases Wiki Activity

prog_util: add guarded buffer allocator

Browse Source
This commit is contained in:
Eric Biggers 2018-12-23 12:34:50 -06:00
parent 57cab078f1
commit a5a4822e2a
2 changed files with 93 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

91
programs/prog_util.c
View File

@ -115,6 +115,97 @@ xmalloc(size_t size)
return p;
}
static size_t
get_page_size(void)
{
#ifdef _WIN32
SYSTEM_INFO info;
GetSystemInfo(&info);
return info.dwPageSize;
#else
return sysconf(_SC_PAGESIZE);
#endif
}
/* Allocate a buffer with guard pages */
int
alloc_guarded_buffer(size_t size, u8 **start_ret, u8 **end_ret)
{
const size_t pagesize = get_page_size();
const size_t nr_pages = (size + pagesize - 1) / pagesize;
u8 *base_addr;
u8 *start, *end;
#ifdef _WIN32
DWORD oldProtect;
#else
int fd;
#endif
*start_ret = NULL;
*end_ret = NULL;
#ifdef _WIN32
/* Allocate buffer and guard pages with no access. */
base_addr = VirtualAlloc(NULL, (nr_pages + 2) * pagesize,
MEM_COMMIT | MEM_RESERVE, PAGE_NOACCESS);
if (!base_addr) {
msg("Unable to allocate memory (VirtualAlloc): Windows error %u",
(unsigned int)GetLastError());
return -1;
}
start = base_addr + pagesize;
end = start + (nr_pages * pagesize);
/* Grant read+write access to just the buffer. */
if (!VirtualProtect(start, end - start, PAGE_READWRITE, &oldProtect)) {
msg("Unable to protect memory (VirtualProtect): Windows error %u",
(unsigned int)GetLastError());
VirtualFree(base_addr, 0, MEM_RELEASE);
return -1;
}
#else
/*
* Allocate buffer and guard pages.
* For portability, use /dev/zero instead of MAP_ANONYMOUS.
*/
fd = open("/dev/zero", O_RDONLY);
if (fd < 0) {
msg_errno("Unable to open /dev/zero");
return -1;
}
base_addr = mmap(NULL, (nr_pages + 2) * pagesize,
PROT_READ|PROT_WRITE, MAP_PRIVATE, fd, 0);
close(fd);
if (base_addr == (u8 *)MAP_FAILED) {
msg_errno("Unable to allocate memory (unable to mmap /dev/zero)");
return -1;
}
start = base_addr + pagesize;
end = start + (nr_pages * pagesize);
/* Unmap the guard pages. */
munmap(base_addr, pagesize);
munmap(end, pagesize);
#endif
*start_ret = start;
*end_ret = end;
return 0;
}
/* Free a buffer that was allocated by alloc_guarded_buffer() */
void
free_guarded_buffer(u8 *start, u8 *end)
{
if (!start)
return;
#ifdef _WIN32
VirtualFree(start - get_page_size(), 0, MEM_RELEASE);
#else
munmap(start, end - start);
#endif
}
/*
* Return the number of timer ticks that have elapsed since some unspecified
* point fixed at the start of program execution

2
programs/prog_util.h
View File

@ -127,6 +127,8 @@ assertion_failed(const char *expr, const char *file, int line);
#define ASSERT(expr) if (!(expr)) assertion_failed(#expr, __FILE__, __LINE__)
extern void *xmalloc(size_t size);
extern int alloc_guarded_buffer(size_t size, u8 **start_ret, u8 **end_ret);
extern void free_guarded_buffer(u8 *start, u8 *end);
extern u64 timer_ticks(void);
extern u64 timer_ticks_to_ms(u64 ticks);