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Date:   Thu, 28 Oct 2021 21:06:30 +0100
From:   Andrew Cooper <andrew.cooper3@...rix.com>
To:     Peter Zijlstra <peterz@...radead.org>, <x86@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>
CC:     <keescook@...omium.org>, <linux-kernel@...r.kernel.org>,
        Mark Rutland <mark.rutland@....com>,
        Will Deacon <will@...nel.org>, <hjl.tools@...il.com>
Subject: Re: [RFC][PATCH] x86: Add straight-line-speculation mitigation

On 28/10/2021 12:44, Peter Zijlstra wrote:
>  arch/x86/Kconfig                              |   12 +++++
>  arch/x86/Makefile                             |    4 +
>  arch/x86/crypto/aegis128-aesni-asm.S          |   48 +++++++++++-----------
>  arch/x86/crypto/aes_ctrby8_avx-x86_64.S       |    2 
>  arch/x86/crypto/aesni-intel_asm.S             |   56 +++++++++++++-------------
>  arch/x86/crypto/aesni-intel_avx-x86_64.S      |   40 +++++++++---------
>  arch/x86/crypto/blake2s-core.S                |    4 -
>  arch/x86/crypto/blowfish-x86_64-asm_64.S      |   12 ++---
>  arch/x86/crypto/camellia-aesni-avx-asm_64.S   |   14 +++---
>  arch/x86/crypto/camellia-aesni-avx2-asm_64.S  |   14 +++---
>  arch/x86/crypto/camellia-x86_64-asm_64.S      |   12 ++---
>  arch/x86/crypto/cast5-avx-x86_64-asm_64.S     |   12 ++---
>  arch/x86/crypto/cast6-avx-x86_64-asm_64.S     |   10 ++--
>  arch/x86/crypto/chacha-avx2-x86_64.S          |    6 +-
>  arch/x86/crypto/chacha-avx512vl-x86_64.S      |    6 +-
>  arch/x86/crypto/chacha-ssse3-x86_64.S         |    8 +--
>  arch/x86/crypto/crc32-pclmul_asm.S            |    2 
>  arch/x86/crypto/crc32c-pcl-intel-asm_64.S     |    2 
>  arch/x86/crypto/crct10dif-pcl-asm_64.S        |    2 
>  arch/x86/crypto/des3_ede-asm_64.S             |    4 -
>  arch/x86/crypto/ghash-clmulni-intel_asm.S     |    6 +-
>  arch/x86/crypto/nh-avx2-x86_64.S              |    2 
>  arch/x86/crypto/nh-sse2-x86_64.S              |    2 
>  arch/x86/crypto/poly1305-x86_64-cryptogams.pl |   38 ++++++++---------
>  arch/x86/crypto/serpent-avx-x86_64-asm_64.S   |   10 ++--
>  arch/x86/crypto/serpent-avx2-asm_64.S         |   10 ++--
>  arch/x86/crypto/serpent-sse2-i586-asm_32.S    |    6 +-
>  arch/x86/crypto/serpent-sse2-x86_64-asm_64.S  |    6 +-
>  arch/x86/crypto/sha1_avx2_x86_64_asm.S        |    2 
>  arch/x86/crypto/sha1_ni_asm.S                 |    2 
>  arch/x86/crypto/sha1_ssse3_asm.S              |    2 
>  arch/x86/crypto/sha256-avx-asm.S              |    2 
>  arch/x86/crypto/sha256-avx2-asm.S             |    2 
>  arch/x86/crypto/sha256-ssse3-asm.S            |    2 
>  arch/x86/crypto/sha256_ni_asm.S               |    2 
>  arch/x86/crypto/sha512-avx-asm.S              |    2 
>  arch/x86/crypto/sha512-avx2-asm.S             |    2 
>  arch/x86/crypto/sha512-ssse3-asm.S            |    2 
>  arch/x86/crypto/sm4-aesni-avx-asm_64.S        |   12 ++---
>  arch/x86/crypto/sm4-aesni-avx2-asm_64.S       |    8 +--
>  arch/x86/crypto/twofish-avx-x86_64-asm_64.S   |   10 ++--
>  arch/x86/crypto/twofish-i586-asm_32.S         |    4 -
>  arch/x86/crypto/twofish-x86_64-asm_64-3way.S  |    6 +-
>  arch/x86/crypto/twofish-x86_64-asm_64.S       |    4 -
>  arch/x86/entry/entry_32.S                     |    2 
>  arch/x86/entry/entry_64.S                     |   12 ++---
>  arch/x86/entry/thunk_32.S                     |    2 
>  arch/x86/entry/thunk_64.S                     |    2 
>  arch/x86/entry/vdso/vdso32/system_call.S      |    2 
>  arch/x86/entry/vdso/vsgx.S                    |    2 
>  arch/x86/entry/vsyscall/vsyscall_emu_64.S     |    6 +-
>  arch/x86/include/asm/linkage.h                |   16 +++++++
>  arch/x86/include/asm/paravirt.h               |    2 
>  arch/x86/include/asm/qspinlock_paravirt.h     |    4 -
>  arch/x86/include/asm/static_call.h            |    2 
>  arch/x86/kernel/acpi/wakeup_32.S              |    6 +-
>  arch/x86/kernel/acpi/wakeup_64.S              |    1 
>  arch/x86/kernel/alternative.c                 |    2 
>  arch/x86/kernel/ftrace.c                      |    2 
>  arch/x86/kernel/ftrace_32.S                   |    6 +-
>  arch/x86/kernel/ftrace_64.S                   |   10 ++--
>  arch/x86/kernel/head_32.S                     |    2 
>  arch/x86/kernel/head_64.S                     |    1 
>  arch/x86/kernel/irqflags.S                    |    2 
>  arch/x86/kernel/paravirt.c                    |    2 
>  arch/x86/kernel/relocate_kernel_32.S          |   10 ++--
>  arch/x86/kernel/relocate_kernel_64.S          |   10 ++--
>  arch/x86/kernel/sev_verify_cbit.S             |    2 
>  arch/x86/kernel/static_call.c                 |    5 +-
>  arch/x86/kernel/verify_cpu.S                  |    4 -
>  arch/x86/kvm/emulate.c                        |    4 -
>  arch/x86/kvm/svm/vmenter.S                    |    4 -
>  arch/x86/kvm/vmx/vmenter.S                    |   14 +++---
>  arch/x86/lib/atomic64_386_32.S                |    2 
>  arch/x86/lib/atomic64_cx8_32.S                |   16 +++----
>  arch/x86/lib/checksum_32.S                    |    8 +--
>  arch/x86/lib/clear_page_64.S                  |    6 +-
>  arch/x86/lib/cmpxchg16b_emu.S                 |    4 -
>  arch/x86/lib/cmpxchg8b_emu.S                  |    4 -
>  arch/x86/lib/copy_mc_64.S                     |    6 +-
>  arch/x86/lib/copy_page_64.S                   |    4 -
>  arch/x86/lib/copy_user_64.S                   |   10 ++--
>  arch/x86/lib/csum-copy_64.S                   |    2 
>  arch/x86/lib/error-inject.c                   |    3 -
>  arch/x86/lib/getuser.S                        |   22 +++++-----
>  arch/x86/lib/hweight.S                        |    6 +-
>  arch/x86/lib/iomap_copy_64.S                  |    2 
>  arch/x86/lib/memcpy_64.S                      |   12 ++---
>  arch/x86/lib/memmove_64.S                     |    4 -
>  arch/x86/lib/memset_64.S                      |    6 +-
>  arch/x86/lib/msr-reg.S                        |    4 -
>  arch/x86/lib/putuser.S                        |    6 +-
>  arch/x86/lib/retpoline.S                      |    6 +-
>  arch/x86/math-emu/div_Xsig.S                  |    2 
>  arch/x86/math-emu/div_small.S                 |    2 
>  arch/x86/math-emu/mul_Xsig.S                  |    6 +-
>  arch/x86/math-emu/polynom_Xsig.S              |    2 
>  arch/x86/math-emu/reg_norm.S                  |    6 +-
>  arch/x86/math-emu/reg_round.S                 |    2 
>  arch/x86/math-emu/reg_u_add.S                 |    2 
>  arch/x86/math-emu/reg_u_div.S                 |    2 
>  arch/x86/math-emu/reg_u_mul.S                 |    2 
>  arch/x86/math-emu/reg_u_sub.S                 |    2 
>  arch/x86/math-emu/round_Xsig.S                |    4 -
>  arch/x86/math-emu/shr_Xsig.S                  |    8 +--
>  arch/x86/math-emu/wm_shrx.S                   |   16 +++----
>  arch/x86/mm/mem_encrypt_boot.S                |    4 -
>  arch/x86/platform/efi/efi_stub_32.S           |    2 
>  arch/x86/platform/efi/efi_stub_64.S           |    2 
>  arch/x86/platform/efi/efi_thunk_64.S          |    2 
>  arch/x86/platform/olpc/xo1-wakeup.S           |    6 +-
>  arch/x86/power/hibernate_asm_32.S             |    4 -
>  arch/x86/power/hibernate_asm_64.S             |    6 +-
>  arch/x86/um/checksum_32.S                     |    4 -
>  arch/x86/um/setjmp_32.S                       |    2 
>  arch/x86/um/setjmp_64.S                       |    2 
>  arch/x86/xen/xen-asm.S                        |   12 ++---
>  arch/x86/xen/xen-head.S                       |    2 
>  samples/ftrace/ftrace-direct-modify.c         |    4 -
>  samples/ftrace/ftrace-direct-too.c            |    2 
>  samples/ftrace/ftrace-direct.c                |    2 
>  scripts/Makefile.lib                          |    3 -
>  tools/objtool/arch/x86/decode.c               |   13 ++++--
>  tools/objtool/builtin-check.c                 |    3 -
>  tools/objtool/check.c                         |   14 ++++++
>  tools/objtool/include/objtool/arch.h          |    1 
>  tools/objtool/include/objtool/builtin.h       |    2 
>  127 files changed, 447 insertions(+), 387 deletions(-)

It would be remiss of me not to say...  In Xen, I've currently gone with:

#ifdef CONFIG_SPECULATIVE_HARDEN_STRAIGHT_LINE
# define ret  ret;  int3
# define retq retq; int3
#endif


which avoids needing to patch any asm files, and therefore is a far less
invasive patch.

I know those defines probably deserve a WTF, and will confuse anyone who
doesn't understand the phrase "painting blue", but they have the
advantage that casual contributions don't need to remember to avoid
naked `ret` instructions to maintain safety, making it a rather more
robust option.

~Andrew

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