csu: Implement and use _dl_early_allocate during static startup
This implements mmap fallback for a brk failure during TLS allocation. scripts/tls-elf-edit.py is updated to support the new patching method. The script no longer requires that in the input object is of ET_DYN type. Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
This commit is contained in:
Florian Weimer
parent
b57ab258c1
commit
f787e138aa
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@ -145,11 +145,16 @@ __libc_setup_tls (void)
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_dl_allocate_tls_storage (in elf/dl-tls.c) does using __libc_memalign
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and dl_tls_static_align. */
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tcb_offset = roundup (memsz + GLRO(dl_tls_static_surplus), max_align);
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tlsblock = __sbrk (tcb_offset + TLS_INIT_TCB_SIZE + max_align);
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tlsblock = _dl_early_allocate (tcb_offset + TLS_INIT_TCB_SIZE + max_align);
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if (tlsblock == NULL)
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_startup_fatal ("Fatal glibc error: Cannot allocate TLS block\n");
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#elif TLS_DTV_AT_TP
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tcb_offset = roundup (TLS_INIT_TCB_SIZE, align ?: 1);
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tlsblock = __sbrk (tcb_offset + memsz + max_align
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+ TLS_PRE_TCB_SIZE + GLRO(dl_tls_static_surplus));
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tlsblock = _dl_early_allocate (tcb_offset + memsz + max_align
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+ TLS_PRE_TCB_SIZE
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+ GLRO(dl_tls_static_surplus));
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if (tlsblock == NULL)
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_startup_fatal ("Fatal glibc error: Cannot allocate TLS block\n");
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tlsblock += TLS_PRE_TCB_SIZE;
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#else
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/* In case a model with a different layout for the TCB and DTV
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19
elf/Makefile
19
elf/Makefile
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@ -33,6 +33,7 @@ routines = \
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$(all-dl-routines) \
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dl-addr \
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dl-addr-obj \
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dl-early_allocate \
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dl-error \
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dl-iteratephdr \
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dl-libc \
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@ -108,6 +109,7 @@ all-dl-routines = $(dl-routines) $(sysdep-dl-routines)
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# But they are absent from the shared libc, because that code is in ld.so.
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elide-routines.os = \
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$(all-dl-routines) \
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dl-early_allocate \
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dl-exception \
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dl-origin \
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dl-reloc-static-pie \
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@ -276,6 +278,7 @@ tests-static-normal := \
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tst-linkall-static \
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tst-single_threaded-pthread-static \
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tst-single_threaded-static \
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tst-tls-allocation-failure-static \
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tst-tlsalign-extern-static \
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tst-tlsalign-static \
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# tests-static-normal
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@ -1213,6 +1216,10 @@ $(objpfx)tst-glibcelf.out: tst-glibcelf.py elf.h $(..)/scripts/glibcelf.py \
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--cc="$(CC) $(patsubst -DMODULE_NAME=%,-DMODULE_NAME=testsuite,$(CPPFLAGS))" \
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< /dev/null > $@ 2>&1; $(evaluate-test)
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ifeq ($(run-built-tests),yes)
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tests-special += $(objpfx)tst-tls-allocation-failure-static-patched.out
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endif
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# The test requires shared _and_ PIE because the executable
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# unit test driver must be able to link with the shared object
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# that is going to eventually go into an installed DSO.
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@ -2937,3 +2944,15 @@ $(eval $(call tst-trace-skeleton,4,\
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$(objpfx)libtracemod2:$(objpfx)libtracemod3:$(objpfx)libtracemod4))
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$(eval $(call tst-trace-skeleton,5,\
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$(objpfx)libtracemod2:$(objpfx)libtracemod3:$(objpfx)libtracemod4:$(objpfx)libtracemod5))
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$(objpfx)tst-tls-allocation-failure-static-patched: \
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$(objpfx)tst-tls-allocation-failure-static $(..)scripts/tst-elf-edit.py
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cp $< $@
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$(PYTHON) $(..)scripts/tst-elf-edit.py --maximize-tls-size $@
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$(objpfx)tst-tls-allocation-failure-static-patched.out: \
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$(objpfx)tst-tls-allocation-failure-static-patched
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$< > $@ 2>&1; echo "status: $$?" >> $@
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grep -q '^Fatal glibc error: Cannot allocate TLS block$$' $@ \
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&& grep -q '^status: 127$$' $@; \
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$(evaluate-test)
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@ -0,0 +1,30 @@
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/* Early memory allocation for the dynamic loader. Generic version.
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Copyright (C) 2022 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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#include <ldsodefs.h>
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#include <stddef.h>
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#include <unistd.h>
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void *
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_dl_early_allocate (size_t size)
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{
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void *result = __sbrk (size);
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if (result == (void *) -1)
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result = NULL;
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return result;
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}
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@ -0,0 +1,31 @@
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/* Base for test program with impossiblyh large PT_TLS segment.
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Copyright (C) 2022 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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/* The test actual binary is patched using scripts/tst-elf-edit.py
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--maximize-tls-size, and this introduces the expected test
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allocation failure due to an excessive PT_LS p_memsz value.
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Patching the binary is required because on some 64-bit targets, TLS
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relocations can only cover a 32-bit range, and glibc-internal TLS
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variables such as errno end up outside that range. */
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int
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main (void)
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{
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return 0;
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}
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@ -43,9 +43,11 @@ EI_DATA=5
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ELFDATA2LSB=b'\x01'
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ELFDATA2MSB=b'\x02'
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ET_EXEC=2
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ET_DYN=3
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PT_LOAD=1
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PT_TLS=7
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def elf_types_fmts(e_ident):
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endian = '<' if e_ident[EI_DATA] == ELFDATA2LSB else '>'
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@ -146,8 +148,15 @@ def elf_edit_align(phdr, align):
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else:
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phdr.p_align = int(align)
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def elf_edit_maximize_tls_size(phdr, elfclass):
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if elfclass == ELFCLASS32:
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# It is possible that the kernel can allocate half of the
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# address space, so use something larger.
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phdr.p_memsz = 0xfff00000
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else:
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phdr.p_memsz = 1 << 63
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def elf_edit(f, align):
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def elf_edit(f, opts):
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ei_nident_fmt = 'c' * EI_NIDENT
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ei_nident_len = struct.calcsize(ei_nident_fmt)
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@ -172,24 +181,35 @@ def elf_edit(f, align):
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ehdr = Elf_Ehdr(e_ident)
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ehdr.read(f)
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if ehdr.e_type != ET_DYN:
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error('{}: not a shared library'.format(f.name))
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if ehdr.e_type not in (ET_EXEC, ET_DYN):
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error('{}: not an executable or shared library'.format(f.name))
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phdr = Elf_Phdr(e_ident)
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maximize_tls_size_done = False
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for i in range(0, ehdr.e_phnum):
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f.seek(ehdr.e_phoff + i * phdr.len)
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phdr.read(f)
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if phdr.p_type == PT_LOAD:
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elf_edit_align(phdr, align)
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if phdr.p_type == PT_LOAD and opts.align is not None:
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elf_edit_align(phdr, opts.align)
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f.seek(ehdr.e_phoff + i * phdr.len)
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phdr.write(f)
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break
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if phdr.p_type == PT_TLS and opts.maximize_tls_size:
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elf_edit_maximize_tls_size(phdr, e_ident[EI_CLASS])
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f.seek(ehdr.e_phoff + i * phdr.len)
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phdr.write(f)
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maximize_tls_size_done = True
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break
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if opts.maximize_tls_size and not maximize_tls_size_done:
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error('{}: TLS maximum size was not updated'.format(f.name))
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def get_parser():
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parser = argparse.ArgumentParser(description=__doc__)
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parser.add_argument('-a', dest='align', required=True,
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parser.add_argument('-a', dest='align',
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help='How to set the LOAD alignment')
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parser.add_argument('--maximize-tls-size', action='store_true',
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help='Set maximum PT_TLS size')
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parser.add_argument('output',
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help='ELF file to edit')
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return parser
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@ -199,7 +219,7 @@ def main(argv):
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parser = get_parser()
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opts = parser.parse_args(argv)
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with open(opts.output, 'r+b') as fout:
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elf_edit(fout, opts.align)
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elf_edit(fout, opts)
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if __name__ == '__main__':
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@ -1211,6 +1211,11 @@ extern struct link_map * _dl_get_dl_main_map (void)
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# endif
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#endif
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/* Perform early memory allocation, avoding a TCB dependency.
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Terminate the process if allocation fails. May attempt to use
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brk. */
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void *_dl_early_allocate (size_t size) attribute_hidden;
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/* Initialize the DSO sort algorithm to use. */
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#if !HAVE_TUNABLES
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static inline void
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@ -0,0 +1,82 @@
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/* Early memory allocation for the dynamic loader. Generic version.
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Copyright (C) 2022 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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/* Mark symbols hidden in static PIE for early self relocation to work. */
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#if BUILD_PIE_DEFAULT
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# pragma GCC visibility push(hidden)
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#endif
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#include <startup.h>
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#include <ldsodefs.h>
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#include <stddef.h>
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#include <string.h>
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#include <sysdep.h>
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#include <unistd.h>
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#include <brk_call.h>
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#include <mmap_call.h>
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/* Defined in brk.c. */
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extern void *__curbrk;
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void *
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_dl_early_allocate (size_t size)
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{
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void *result;
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if (__curbrk != NULL)
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/* If the break has been initialized, brk must have run before,
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so just call it once more. */
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{
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result = __sbrk (size);
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if (result == (void *) -1)
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result = NULL;
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}
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else
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{
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/* If brk has not been invoked, there is no need to update
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__curbrk. The first call to brk will take care of that. */
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void *previous = __brk_call (0);
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result = __brk_call (previous + size);
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if (result == previous)
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result = NULL;
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else
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result = previous;
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}
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/* If brk fails, fall back to mmap. This can happen due to
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unfortunate ASLR layout decisions and kernel bugs, particularly
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for static PIE. */
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if (result == NULL)
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{
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long int ret;
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int prot = PROT_READ | PROT_WRITE;
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int flags = MAP_PRIVATE | MAP_ANONYMOUS;
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#ifdef __NR_mmap2
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ret = MMAP_CALL_INTERNAL (mmap2, 0, size, prot, flags, -1, 0);
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#else
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ret = MMAP_CALL_INTERNAL (mmap, 0, size, prot, flags, -1, 0);
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#endif
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if (INTERNAL_SYSCALL_ERROR_P (ret))
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result = NULL;
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else
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result = (void *) ret;
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}
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return result;
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}
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