On Mon, Oct 23, 2023 at 10:08:33AM +0200, Arnd Bergmann wrote: > On Mon, Oct 23, 2023, at 09:57, Maria Yu wrote: > > Module PLT feature can be enabled even when RANDOM_BASE is disabled. > > Break BLT entry counts of relocation types will make module plt entry > > allocation fail and finally exec format error for even correct and plt > > allocation available modules. Has an actual problem been seen in practice, or was this found by looking at the code? > > > > Signed-off-by: Maria Yu <quic_aiquny@xxxxxxxxxxx> > > Adding Ard Biesheuvel to Cc, as he added the check in commit > a257e02579e42 ("arm64/kernel: don't ban ADRP to work around > Cortex-A53 erratum #843419") I think that the actual mistake is in commit: 3e35d303ab7d22c4 ("arm64: module: rework module VA range selection") Prior to that commit, when CONFIG_RANDOMIZE_BASE=n all modules and code had to be within 128M of each other, and so there were no PLTs necessary for B/BL. After that commit we can have a 2G module range regardless of CONFIG_RANDOMIZE_BASE, and PLTs may be necessary for B/BL. We should have removed the check for !CONFIG_RANDOMIZE_BASE as part of that. > > arch/arm64/kernel/module-plts.c | 3 --- > > 1 file changed, 3 deletions(-) > > > > diff --git a/arch/arm64/kernel/module-plts.c > > b/arch/arm64/kernel/module-plts.c > > index bd69a4e7cd60..21a67d52d7a0 100644 > > --- a/arch/arm64/kernel/module-plts.c > > +++ b/arch/arm64/kernel/module-plts.c > > @@ -167,9 +167,6 @@ static unsigned int count_plts(Elf64_Sym *syms, > > Elf64_Rela *rela, int num, > > switch (ELF64_R_TYPE(rela[i].r_info)) { > > case R_AARCH64_JUMP26: > > case R_AARCH64_CALL26: > > - if (!IS_ENABLED(CONFIG_RANDOMIZE_BASE)) > > - break; > > - > > /* > > * We only have to consider branch targets that resolve > > * to symbols that are defined in a different section. > > I see there are two such checks (in partition_branch_plt_relas() > and in count_plts()), can you explain in more detail how you > concluded that one of them is correct but the other one is not? I believe that the one in partition_branch_plt_relas() needs to go too; that's just a minor optimization for the case where there shouldn't be any PLTs for B/BL, and it no longer holds after the module VA range rework. That was introduced in commit: d4e0340919fb9190 ("arm64/module: Optimize module load time by optimizing PLT counting") Thanks, Mark.