From d5aaece8a3528ff5f9cc0ceeb067da0e47436669 Mon Sep 17 00:00:00 2001
From: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Date: Tue, 3 Jan 2023 09:56:28 -0300
Subject: [PATCH 185/185] elf: Fix GL(dl_phdr) and GL(dl_phnum) for static
builds [BZ #29864]
The 73fc4e28b9464f0e refactor did not add the GL(dl_phdr) and
GL(dl_phnum) for static build, relying on the __ehdr_start symbol,
which is always added by the static linker, to get the correct values.
This is problematic in some ways:
- The segment may see its in-memory size differ from its in-file
size (or the binary may have holes). The Linux has fixed is to
provide concise values for both AT_PHDR and AT_PHNUM (commit
0da1d5002745c - "fs/binfmt_elf: Fix AT_PHDR for unusual ELF files")
- Some archs (alpha for instance) the hidden weak reference is not
correctly pulled by the static linker and __ehdr_start address
end up being 0, which makes GL(dl_phdr) and GL(dl_phnum) have both
invalid values (and triggering a segfault later on libc.so while
accessing TLS variables).
The safer fix is to just restore the previous behavior to setup
GL(dl_phdr) and GL(dl_phnum) for static based on kernel auxv. The
__ehdr_start fallback can also be simplified by not assuming weak
linkage (as for PIE).
The libc-static.c auxv init logic is moved to dl-support.c, since
the later is build without SHARED and then GLRO macro is defined
to access the variables directly.
The _dl_phdr is also assumed to be always non NULL, since an invalid
NULL values does not trigger TLS initialization (which is used in
various libc systems).
Checked on aarch64-linux-gnu, x86_64-linux-gnu, and i686-linux-gnu.
Reviewed-by: Florian Weimer <fweimer@redhat.com>
(cherry picked from commit 7e31d166510ac4adbf53d5e8144c709a37dd8c7a)
---
NEWS | 2 ++
csu/libc-start.c | 21 ---------------------
csu/libc-tls.c | 25 ++++++++++++-------------
elf/dl-support.c | 46 ++++++++++++++++++++++++++++++++--------------
4 files changed, 46 insertions(+), 48 deletions(-)
diff --git a/NEWS b/NEWS
index 8c79e83b775c..c5e142eb3a5d 100644
--- a/NEWS
+++ b/NEWS
@@ -26,6 +26,8 @@ The following bugs are resolved with this release:
[12154] Do not fail DNS resolution for CNAMEs which are not host names
[24816] Fix tst-nss-files-hosts-long on single-stack hosts
[28846] CMSG_NXTHDR may trigger -Wstrict-overflow warning
+ [29864] libc: __libc_start_main() should obtain program headers
+ address (_dl_phdr) from the auxv, not the ELF header.
[29305] Conserve NSS buffer space during DNS packet parsing
[29402] nscd: nscd: No such file or directory
[29415] nscd: Fix netlink cache invalidation if epoll is used
diff --git a/csu/libc-start.c b/csu/libc-start.c
index 543560f36c33..bfeee6d8513f 100644
--- a/csu/libc-start.c
+++ b/csu/libc-start.c
@@ -262,28 +262,7 @@ LIBC_START_MAIN (int (*main) (int, char **, char ** MAIN_AUXVEC_DECL),
}
# endif
_dl_aux_init (auxvec);
- if (GL(dl_phdr) == NULL)
# endif
- {
- /* Starting from binutils-2.23, the linker will define the
- magic symbol __ehdr_start to point to our own ELF header
- if it is visible in a segment that also includes the phdrs.
- So we can set up _dl_phdr and _dl_phnum even without any
- information from auxv. */
-
- extern const ElfW(Ehdr) __ehdr_start
-# if BUILD_PIE_DEFAULT
- __attribute__ ((visibility ("hidden")));
-# else
- __attribute__ ((weak, visibility ("hidden")));
- if (&__ehdr_start != NULL)
-# endif
- {
- assert (__ehdr_start.e_phentsize == sizeof *GL(dl_phdr));
- GL(dl_phdr) = (const void *) &__ehdr_start + __ehdr_start.e_phoff;
- GL(dl_phnum) = __ehdr_start.e_phnum;
- }
- }
__tunables_init (__environ);
diff --git a/csu/libc-tls.c b/csu/libc-tls.c
index 0a216c550289..7fdf7cd7a84d 100644
--- a/csu/libc-tls.c
+++ b/csu/libc-tls.c
@@ -118,19 +118,18 @@ __libc_setup_tls (void)
__tls_pre_init_tp ();
/* Look through the TLS segment if there is any. */
- if (_dl_phdr != NULL)
- for (phdr = _dl_phdr; phdr < &_dl_phdr[_dl_phnum]; ++phdr)
- if (phdr->p_type == PT_TLS)
- {
- /* Remember the values we need. */
- memsz = phdr->p_memsz;
- filesz = phdr->p_filesz;
- initimage = (void *) phdr->p_vaddr + main_map->l_addr;
- align = phdr->p_align;
- if (phdr->p_align > max_align)
- max_align = phdr->p_align;
- break;
- }
+ for (phdr = _dl_phdr; phdr < &_dl_phdr[_dl_phnum]; ++phdr)
+ if (phdr->p_type == PT_TLS)
+ {
+ /* Remember the values we need. */
+ memsz = phdr->p_memsz;
+ filesz = phdr->p_filesz;
+ initimage = (void *) phdr->p_vaddr + main_map->l_addr;
+ align = phdr->p_align;
+ if (phdr->p_align > max_align)
+ max_align = phdr->p_align;
+ break;
+ }
/* Calculate the size of the static TLS surplus, with 0 auditors. */
_dl_tls_static_surplus_init (0);
diff --git a/elf/dl-support.c b/elf/dl-support.c
index 4af0b5b2ce23..f45b630ba5cf 100644
--- a/elf/dl-support.c
+++ b/elf/dl-support.c
@@ -255,6 +255,25 @@ _dl_aux_init (ElfW(auxv_t) *av)
for (int i = 0; i < array_length (auxv_values); ++i)
auxv_values[i] = 0;
_dl_parse_auxv (av, auxv_values);
+
+ _dl_phdr = (void*) auxv_values[AT_PHDR];
+ _dl_phnum = auxv_values[AT_PHNUM];
+
+ if (_dl_phdr == NULL)
+ {
+ /* Starting from binutils-2.23, the linker will define the
+ magic symbol __ehdr_start to point to our own ELF header
+ if it is visible in a segment that also includes the phdrs.
+ So we can set up _dl_phdr and _dl_phnum even without any
+ information from auxv. */
+
+ extern const ElfW(Ehdr) __ehdr_start attribute_hidden;
+ assert (__ehdr_start.e_phentsize == sizeof *GL(dl_phdr));
+ _dl_phdr = (const void *) &__ehdr_start + __ehdr_start.e_phoff;
+ _dl_phnum = __ehdr_start.e_phnum;
+ }
+
+ assert (_dl_phdr != NULL);
}
#endif
@@ -323,20 +342,19 @@ _dl_non_dynamic_init (void)
if (_dl_platform != NULL)
_dl_platformlen = strlen (_dl_platform);
- if (_dl_phdr != NULL)
- for (const ElfW(Phdr) *ph = _dl_phdr; ph < &_dl_phdr[_dl_phnum]; ++ph)
- switch (ph->p_type)
- {
- /* Check if the stack is nonexecutable. */
- case PT_GNU_STACK:
- _dl_stack_flags = ph->p_flags;
- break;
-
- case PT_GNU_RELRO:
- _dl_main_map.l_relro_addr = ph->p_vaddr;
- _dl_main_map.l_relro_size = ph->p_memsz;
- break;
- }
+ for (const ElfW(Phdr) *ph = _dl_phdr; ph < &_dl_phdr[_dl_phnum]; ++ph)
+ switch (ph->p_type)
+ {
+ /* Check if the stack is nonexecutable. */
+ case PT_GNU_STACK:
+ _dl_stack_flags = ph->p_flags;
+ break;
+
+ case PT_GNU_RELRO:
+ _dl_main_map.l_relro_addr = ph->p_vaddr;
+ _dl_main_map.l_relro_size = ph->p_memsz;
+ break;
+ }
call_function_static_weak (_dl_find_object_init);
--
2.39.1
