On Tue, Oct 26, 2021 at 02:01:32PM +0200, Peter Zijlstra wrote:
> Hi,
>
> These patches rewrite the way retpolines are rewritten. Currently objtool emits
> alternative entries for most retpoline calls. However trying to extend that led
> to trouble (ELF files are horrid).
>
> Therefore completely overhaul this and have objtool emit a .retpoline_sites
> section that lists all compiler generated retpoline thunk calls. Then the
> kernel can do with them as it pleases.
>
> Notably it will:
>
> - rewrite them to indirect instructions for !RETPOLINE
> - rewrite them to lfence; indirect; for RETPOLINE_AMD,
> where size allows (boo clang!)
>
> Specifically, the !RETPOLINE case can now also deal with the clang-special
> conditional-indirect-tail-call:
>
> Jcc __x86_indirect_thunk_\reg.
>
> Finally, also update the x86 BPF jit to catch up to recent times and do these
> same things.
>
> All this should help improve performance by removing an indirection.
>
> Patches can (soon) be found here:
>
> git://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git objtool/core
>
> Changes since v2:
>
> - rewrite the __x86_indirect_thunk_array[] stuff again
> - rewrite the retpoline,amd rewrite logic, it now also supports
> rewriting the Jcc case, if the original instruction is long enough, but
> more importantly, it's simpler code.
> - bpf label simplification patch
> - random assorted cleanups
> - actually managed to get bpf selftests working
>
> ---
> arch/um/kernel/um_arch.c | 4 +
> arch/x86/include/asm/GEN-for-each-reg.h | 14 ++-
> arch/x86/include/asm/alternative.h | 1 +
> arch/x86/include/asm/asm-prototypes.h | 18 ---
> arch/x86/include/asm/nospec-branch.h | 72 ++---------
> arch/x86/kernel/alternative.c | 189 ++++++++++++++++++++++++++++-
> arch/x86/kernel/cpu/bugs.c | 7 --
> arch/x86/kernel/module.c | 9 +-
> arch/x86/kernel/vmlinux.lds.S | 14 +++
> arch/x86/lib/retpoline.S | 56 ++-------
> arch/x86/net/bpf_jit_comp.c | 160 +++++++++---------------
> arch/x86/net/bpf_jit_comp32.c | 22 +++-
> tools/objtool/arch/x86/decode.c | 120 ------------------
> tools/objtool/check.c | 208 ++++++++++++++++++++++----------
> tools/objtool/elf.c | 84 -------------
> tools/objtool/include/objtool/check.h | 1 -
> tools/objtool/include/objtool/elf.h | 6 +-
> tools/objtool/special.c | 8 --
> 18 files changed, 472 insertions(+), 521 deletions(-)
Ok, this all looks real nice, thx!
Reviewed-by: Borislav Petkov <bp@xxxxxxx>
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
