On Thu, 9 Dec 2021 08:38:17 +0100 Alexander Egorenkov <egorenar@xxxxxxxxxxxxx> wrote: > 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> Thanks! Reviewed-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);
