Starting with gcc 11.3, the C compiler will generate PLT-relative function calls even if they are local and do not require it. Later on during linking, the linker will replace all PLT-relative calls to local functions with PC-relative ones. Unfortunately, the purgatory code of kexec/kdump is not being linked as a regular executable or shared library would have been, and therefore, all PLT-relative addresses remain in the generated purgatory object code unresolved. This leads to the situation where the purgatory code is being executed during kdump with all PLT-relative addresses unresolved. And this results in endless loops within the purgatory code. Furthermore, the clang C compiler has always behaved like described above and this commit should fix kdump for kernels built with the latter. Because the purgatory code is no regular executable or shared library, contains only calls to local functions and has no PLT, all R_390_PLT32DBL relocation entries can be resolved just like a R_390_PC32DBL one. * https://refspecs.linuxfoundation.org/ELF/zSeries/lzsabi0_zSeries/x1633.html#AEN1699 Relocation entries of purgatory code generated with gcc 11.3 ------------------------------------------------------------ $ readelf -r linux/arch/s390/purgatory/purgatory.o Relocation section '.rela.text' at offset 0x370 contains 5 entries: Offset Info Type Sym. Value Sym. Name + Addend 00000000005c 000c00000013 R_390_PC32DBL 0000000000000000 purgatory_sha_regions + 2 00000000007a 000d00000014 R_390_PLT32DBL 0000000000000000 sha256_update + 2 00000000008c 000e00000014 R_390_PLT32DBL 0000000000000000 sha256_final + 2 000000000092 000800000013 R_390_PC32DBL 0000000000000000 .LC0 + 2 0000000000a0 000f00000014 R_390_PLT32DBL 0000000000000000 memcmp + 2 Relocation entries of purgatory code generated with gcc 11.2 ------------------------------------------------------------ $ readelf -r linux/arch/s390/purgatory/purgatory.o Relocation section '.rela.text' at offset 0x368 contains 5 entries: Offset Info Type Sym. Value Sym. Name + Addend 00000000005c 000c00000013 R_390_PC32DBL 0000000000000000 purgatory_sha_regions + 2 00000000007a 000d00000013 R_390_PC32DBL 0000000000000000 sha256_update + 2 00000000008c 000e00000013 R_390_PC32DBL 0000000000000000 sha256_final + 2 000000000092 000800000013 R_390_PC32DBL 0000000000000000 .LC0 + 2 0000000000a0 000f00000013 R_390_PC32DBL 0000000000000000 memcmp + 2 Signed-off-by: Alexander Egorenkov <egorenar@xxxxxxxxxxxxx> Reported-by: Tao Liu <ltao@xxxxxxxxxx> Suggested-by: Philipp Rudo <prudo@xxxxxxxxxx> --- Changes since v1: ================= * Alternative version of the fix but this time in arch_kexec_apply_relocations_add() in order not to force every user of arch_kexec_do_relocs() to handle R_390_PC32DBL and avoid breaking other users with unexpected bhavior arch/s390/kernel/machine_kexec_file.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/arch/s390/kernel/machine_kexec_file.c b/arch/s390/kernel/machine_kexec_file.c index 876cdd3c994e..8f43575a4dd3 100644 --- a/arch/s390/kernel/machine_kexec_file.c +++ b/arch/s390/kernel/machine_kexec_file.c @@ -348,6 +348,10 @@ int arch_kexec_apply_relocations_add(struct purgatory_info *pi, addr = section->sh_addr + relas[i].r_offset; r_type = ELF64_R_TYPE(relas[i].r_info); + + if (r_type == R_390_PLT32DBL) + r_type = R_390_PC32DBL; + ret = arch_kexec_do_relocs(r_type, loc, val, addr); if (ret) { pr_err("Unknown rela relocation: %d\n", r_type); -- 2.31.1
