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| author | Florian Weimer <fweimer@redhat.com> | 2021-02-25 12:10:57 +0100 |
|---|---|---|
| committer | Florian Weimer <fweimer@redhat.com> | 2021-02-25 12:13:02 +0100 |
| commit | 035c012e32c11e84d64905efaf55e74f704d3668 (patch) | |
| tree | 7b08a9e9cbd8e4dd2e420cd6b7c204aeb5d61ccc /sysdeps/i386 | |
| parent | a79328c745219dcb395070cdcd3be065a8347f24 (diff) | |
| download | glibc-035c012e32c11e84d64905efaf55e74f704d3668.tar.gz glibc-035c012e32c11e84d64905efaf55e74f704d3668.tar.xz glibc-035c012e32c11e84d64905efaf55e74f704d3668.zip | |
Reduce the statically linked startup code [BZ #23323]
It turns out the startup code in csu/elf-init.c has a perfect pair of ROP gadgets (see Marco-Gisbert and Ripoll-Ripoll, "return-to-csu: A New Method to Bypass 64-bit Linux ASLR"). These functions are not needed in dynamically-linked binaries because DT_INIT/DT_INIT_ARRAY are already processed by the dynamic linker. However, the dynamic linker skipped the main program for some reason. For maximum backwards compatibility, this is not changed, and instead, the main map is consulted from __libc_start_main if the init function argument is a NULL pointer. For statically linked binaries, the old approach based on linker symbols is still used because there is nothing else available. A new symbol version __libc_start_main@@GLIBC_2.34 is introduced because new binaries running on an old libc would not run their ELF constructors, leading to difficult-to-debug issues.
Diffstat (limited to 'sysdeps/i386')
| -rw-r--r-- | sysdeps/i386/start.S | 14 |
1 files changed, 6 insertions, 8 deletions
diff --git a/sysdeps/i386/start.S b/sysdeps/i386/start.S index 24c806cfec..5296b27e65 100644 --- a/sysdeps/i386/start.S +++ b/sysdeps/i386/start.S @@ -87,11 +87,9 @@ ENTRY (_start) call 1f addl $_GLOBAL_OFFSET_TABLE_, %ebx - /* Push address of our own entry points to .fini and .init. */ - leal __libc_csu_fini@GOTOFF(%ebx), %eax - pushl %eax - leal __libc_csu_init@GOTOFF(%ebx), %eax - pushl %eax + /* This used to be the addresses of .fini and .init. */ + pushl $0 + pushl $0 pushl %ecx /* Push second argument: argv. */ pushl %esi /* Push first argument: argc. */ @@ -112,9 +110,9 @@ ENTRY (_start) But let the libc call main. */ call __libc_start_main@PLT #else - /* Push address of our own entry points to .fini and .init. */ - pushl $__libc_csu_fini - pushl $__libc_csu_init + /* This used to be the addresses of .fini and .init. */ + pushl $0 + pushl $0 pushl %ecx /* Push second argument: argv. */ pushl %esi /* Push first argument: argc. */ |