bFLT binaries are usually created using elf2flt.
The linker script used by elf2flt has defined the .data section like the
following for the last 19 years:
.data : {
_sdata = . ;
__data_start = . ;
data_start = . ;
*(.got.plt)
*(.got)
FILL(0) ;
. = ALIGN(0x20) ;
LONG(-1)
. = ALIGN(0x20) ;
...
}
It places the .got.plt input section before the .got input section.
The same is true for the default linker script (ld --verbose) on most
architectures except x86/x86-64.
The binfmt_flat loader should relocate all GOT entries until it encounters
a -1 (the LONG(-1) in the linker script).
The problem is that the .got.plt input section starts with a GOTPLT header
that has the first word (two u32 entries for 64-bit archs) set to -1.
See e.g. the binutils implementation for architectures [1] [2] [3] [4].
This causes the binfmt_flat loader to stop relocating GOT entries
prematurely and thus causes the application to crash when running.
Fix this by ignoring -1 in the first two u32 entries in the .data section.
A -1 will only be ignored for the first two entries for bFLT binaries with
FLAT_FLAG_GOTPIC set, which is unconditionally set by elf2flt if the
supplied ELF binary had the symbol _GLOBAL_OFFSET_TABLE_ defined, therefore
ELF binaries without a .got input section should remain unaffected.
Tested on RISC-V Canaan Kendryte K210 and RISC-V QEMU nommu_virt_defconfig.
[1] https://sourceware.org/git/?p=binutils-gdb.git;a=blob;f=bfd/elfnn-riscv.c;hb=binutils-2_38#l3275
[2] https://sourceware.org/git/?p=binutils-gdb.git;a=blob;f=bfd/elfxx-tilegx.c;hb=binutils-2_38#l4023
[3] https://sourceware.org/git/?p=binutils-gdb.git;a=blob;f=bfd/elf32-tilepro.c;hb=binutils-2_38#l3633
[4] https://sourceware.org/git/?p=binutils-gdb.git;a=blob;f=bfd/elfnn-loongarch.c;hb=binutils-2_38#l2978
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Niklas Cassel <niklas.cassel@xxxxxxx>
---
RISC-V elf2flt patches are still not merged, they can be found here:
https://github.com/floatious/elf2flt/tree/riscv
buildroot branch for k210 nommu (including this patch and elf2flt patches):
https://github.com/floatious/buildroot/tree/k210-v14
fs/binfmt_flat.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)
diff --git a/fs/binfmt_flat.c b/fs/binfmt_flat.c
index 626898150011..b80009e6392e 100644
--- a/fs/binfmt_flat.c
+++ b/fs/binfmt_flat.c
@@ -793,8 +793,17 @@ static int load_flat_file(struct linux_binprm *bprm,
u32 addr, rp_val;
if (get_user(rp_val, rp))
return -EFAULT;
- if (rp_val == 0xffffffff)
+ /*
+ * The first word in the GOTPLT header is -1 on certain
+ * architechtures. (On 64-bit, that is two u32 entries.)
+ * Ignore these entries, so that we stop relocating GOT
+ * entries first when we encounter the -1 after the GOT.
+ */
+ if (rp_val == 0xffffffff) {
+ if (rp - (u32 __user *)datapos < 2)
+ continue;
break;
+ }
if (rp_val) {
addr = calc_reloc(rp_val, libinfo, id, 0);
if (addr == RELOC_FAILED) {
--
2.35.1
