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author | Szabolcs Nagy <szabolcs.nagy@arm.com> | 2020-12-01 10:13:18 +0000 |
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committer | Szabolcs Nagy <szabolcs.nagy@arm.com> | 2020-12-02 08:48:08 +0000 |
commit | 924e11d5169890a0c78e745467844eea922d5f98 (patch) | |
tree | ed7bfd067593ba56ea76be6c89cd8569baaffdc9 /sysdeps/aarch64/dl-bti.c | |
parent | a05a7f7505d44109533d17e151f6ae88d688b1e8 (diff) | |
download | glibc-nsz/btifix-v3.tar.gz glibc-nsz/btifix-v3.tar.xz glibc-nsz/btifix-v3.zip |
aarch64: Use mmap to add PROT_BTI instead of mprotect [BZ #26831] nsz/btifix-v3
Re-mmap executable segments if possible instead of using mprotect to add PROT_BTI. This allows using BTI protection with security policies that prevent mprotect with PROT_EXEC. If the fd of the ELF module is not available because it was kernel mapped then mprotect is used and failures are ignored. To protect the main executable even when mprotect is filtered the linux kernel will have to be changed to add PROT_BTI to it. The delayed failure reporting is mainly needed because currently _dl_process_gnu_properties does not propagate failures such that the required cleanups happen. Using the link_map_machine struct for error propagation is not ideal, but this seemed to be the least intrusive solution. Fixes bug 26831.
Diffstat (limited to 'sysdeps/aarch64/dl-bti.c')
-rw-r--r-- | sysdeps/aarch64/dl-bti.c | 54 |
1 files changed, 36 insertions, 18 deletions
diff --git a/sysdeps/aarch64/dl-bti.c b/sysdeps/aarch64/dl-bti.c index 67d63c8a73..ff26c98ccf 100644 --- a/sysdeps/aarch64/dl-bti.c +++ b/sysdeps/aarch64/dl-bti.c @@ -19,9 +19,17 @@ #include <errno.h> #include <libintl.h> #include <ldsodefs.h> +#include <sys/mman.h> -static void -enable_bti (struct link_map *map, const char *program) +/* See elf/dl-load.h. */ +#ifndef MAP_COPY +# define MAP_COPY (MAP_PRIVATE | MAP_DENYWRITE) +#endif + +/* Enable BTI protection for MAP. */ + +void +_dl_bti_protect (struct link_map *map, int fd) { const size_t pagesz = GLRO(dl_pagesize); const ElfW(Phdr) *phdr; @@ -41,19 +49,31 @@ enable_bti (struct link_map *map, const char *program) if (phdr->p_flags & PF_W) prot |= PROT_WRITE; - if (__mprotect (start, len, prot) < 0) - { - if (program) - _dl_fatal_printf ("%s: mprotect failed to turn on BTI\n", - map->l_name); - else - _dl_signal_error (errno, map->l_name, "dlopen", - N_("mprotect failed to turn on BTI")); - } + if (fd == -1) + /* Ignore failures for kernel mapped binaries. */ + __mprotect (start, len, prot); + else + map->l_mach.bti_fail = __mmap (start, len, prot, + MAP_FIXED|MAP_COPY|MAP_FILE, + fd, off) == MAP_FAILED; } } -/* Enable BTI for MAP and its dependencies. */ + +static void +bti_failed (struct link_map *l, const char *program) +{ + if (program) + _dl_fatal_printf ("%s: %s: failed to turn on BTI protection\n", + program, l->l_name); + else + /* Note: the errno value is not available any more. */ + _dl_signal_error (0, l->l_name, "dlopen", + N_("failed to turn on BTI protection")); +} + + +/* Report BTI protection failures for MAP and its dependencies. */ void _dl_bti_check (struct link_map *map, const char *program) @@ -61,16 +81,14 @@ _dl_bti_check (struct link_map *map, const char *program) if (!GLRO(dl_aarch64_cpu_features).bti) return; - if (map->l_mach.bti) - enable_bti (map, program); + if (map->l_mach.bti_fail) + bti_failed (map, program); unsigned int i = map->l_searchlist.r_nlist; while (i-- > 0) { struct link_map *l = map->l_initfini[i]; - if (l->l_init_called) - continue; - if (l->l_mach.bti) - enable_bti (l, program); + if (l->l_mach.bti_fail) + bti_failed (l, program); } } |