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rtld-elf: support either byte-order of hints file

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Accept either little-endian or big-endian representation of the ELF
hints magic number in the header of a hints file and convert the
parameters to the native byte-order of the repsective system.

This is a pre-requisite for a planned change to always write the byte
order in little-endian format on all architectures. The only relvant
architecture that uses big-endian data is powerpc64, and it is not
likely that new architectures will choose that representation of data
in memory.

When all supported architectures use little-endian data in the hints
file, the byte swap logic can be enabled for big-endian CPUs at
compile time. Up to that point, there is a very small run-time penalty
that is paid on all systems to check the byte-order of the hints file
and to provide the option to byte-swap the parameters read from the
hints file header.

This commit contains the changes from review D44080 (which had been
split off from this patch for easier review),

Reviewed by:	kib
MFC after:	1 month
Differential Revision:	https://reviews.freebsd.org/D44053
This commit is contained in:
Stefan Eßer 2024-02-26 23:18:12 +01:00
parent 975d773082
commit 7b77d37a56
1 changed files with 60 additions and 16 deletions
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76
libexec/rtld-elf/rtld.c
View file

@ -2050,6 +2050,9 @@ find_symdef(unsigned long symnum, const Obj_Entry *refobj,
return (def);
}
/* Convert between native byte order and forced little resp. big endian. */
#define COND_SWAP(n) (is_le ? le32toh(n) : be32toh(n))
/*
* Return the search path from the ldconfig hints file, reading it if
* necessary. If nostdlib is true, then the default search paths are
@ -2073,6 +2076,12 @@ gethints(bool nostdlib)
int fd;
size_t flen;
uint32_t dl;
uint32_t magic; /* Magic number */
uint32_t version; /* File version (1) */
uint32_t strtab; /* Offset of string table in file */
uint32_t dirlist; /* Offset of directory list in string table */
uint32_t dirlistlen; /* strlen(dirlist) */
bool is_le;
bool skip;
/* First call, read the hints file */
@ -2080,8 +2089,10 @@ gethints(bool nostdlib)
/* Keep from trying again in case the hints file is bad. */
hints = "";
if ((fd = open(ld_elf_hints_path, O_RDONLY | O_CLOEXEC)) == -1)
if ((fd = open(ld_elf_hints_path, O_RDONLY | O_CLOEXEC)) == -1) {
dbg("failed to open hints file \"%s\"", ld_elf_hints_path);
return (NULL);
}
/*
* Check of hdr.dirlistlen value against type limit
@ -2089,29 +2100,62 @@ gethints(bool nostdlib)
* paranoia leads to checks that dirlist is fully
* contained in the file range.
*/
if (read(fd, &hdr, sizeof hdr) != sizeof hdr ||
hdr.magic != ELFHINTS_MAGIC ||
hdr.version != 1 || hdr.dirlistlen > UINT_MAX / 2 ||
fstat(fd, &hint_stat) == -1) {
if (read(fd, &hdr, sizeof hdr) != sizeof hdr) {
dbg("failed to read %lu bytes from hints file \"%s\"",
(u_long)sizeof hdr, ld_elf_hints_path);
cleanup1:
close(fd);
hdr.dirlistlen = 0;
return (NULL);
}
dl = hdr.strtab;
if (dl + hdr.dirlist < dl)
is_le = /*le32toh(1) == 1 || */ hdr.magic == ELFHINTS_MAGIC;
magic = COND_SWAP(hdr.magic);
version = COND_SWAP(hdr.version);
strtab = COND_SWAP(hdr.strtab);
dirlist = COND_SWAP(hdr.dirlist);
dirlistlen = COND_SWAP(hdr.dirlistlen);
if (magic != ELFHINTS_MAGIC) {
dbg("invalid magic number %#08x (expected: %#08x)",
magic, ELFHINTS_MAGIC);
goto cleanup1;
dl += hdr.dirlist;
if (dl + hdr.dirlistlen < dl)
}
if (version != 1) {
dbg("hints file version %d (expected: 1)", version);
goto cleanup1;
dl += hdr.dirlistlen;
if (dl > hint_stat.st_size)
}
if (dirlistlen > UINT_MAX / 2) {
dbg("directory list is to long: %d > %d",
dirlistlen, UINT_MAX / 2);
goto cleanup1;
p = xmalloc(hdr.dirlistlen + 1);
if (pread(fd, p, hdr.dirlistlen + 1,
hdr.strtab + hdr.dirlist) != (ssize_t)hdr.dirlistlen + 1 ||
p[hdr.dirlistlen] != '\0') {
}
if (fstat(fd, &hint_stat) == -1) {
dbg("failed to find length of hints file \"%s\"",
ld_elf_hints_path);
goto cleanup1;
}
dl = strtab;
if (dl + dirlist < dl) {
dbg("invalid string table position %d", dl);
goto cleanup1;
}
dl += dirlist;
if (dl + dirlistlen < dl) {
dbg("invalid directory list offset %d", dirlist);
goto cleanup1;
}
dl += dirlistlen;
if (dl > hint_stat.st_size) {
dbg("hints file \"%s\" is truncated (%d vs. %jd bytes)",
ld_elf_hints_path, dl, (uintmax_t)hint_stat.st_size);
goto cleanup1;
}
p = xmalloc(dirlistlen + 1);
if (pread(fd, p, dirlistlen + 1,
strtab + dirlist) != (ssize_t)dirlistlen + 1 ||
p[dirlistlen] != '\0') {
free(p);
dbg("failed to read %d bytes starting at %d from hints file \"%s\"",
dirlistlen + 1, strtab + dirlist, ld_elf_hints_path);
goto cleanup1;
}
hints = p;
@ -2174,7 +2218,7 @@ gethints(bool nostdlib)
*/
fndx = 0;
fcount = 0;
filtered_path = xmalloc(hdr.dirlistlen + 1);
filtered_path = xmalloc(dirlistlen + 1);
hintpath = &hintinfo->dls_serpath[0];
for (hintndx = 0; hintndx < hmeta.dls_cnt; hintndx++, hintpath++) {
skip = false;