Messages in this thread | | | From | Sedat Dilek <> | Date | Fri, 1 Oct 2021 22:55:22 +0200 | Subject | Re: [PATCH v4 00/15] x86: Add support for Clang CFI |
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On Thu, Sep 30, 2021 at 8:38 PM Nick Desaulniers <ndesaulniers@google.com> wrote: > > On Thu, Sep 30, 2021 at 11:05 AM Sami Tolvanen <samitolvanen@google.com> wrote: > > > > This series adds support for Clang's Control-Flow Integrity (CFI) > > checking to x86_64. With CFI, the compiler injects a runtime > > check before each indirect function call to ensure the target is > > a valid function with the correct static type. This restricts > > possible call targets and makes it more difficult for an attacker > > to exploit bugs that allow the modification of stored function > > pointers. For more details, see: > > > > https://clang.llvm.org/docs/ControlFlowIntegrity.html > > > > Note that v4 is based on tip/master. The first two patches contain > > objtool support for CFI, the remaining patches change function > > declarations to use opaque types, fix type mismatch issues that > > confuse the compiler, and disable CFI where it can't be used. > > > > You can also pull this series from > > > > https://github.com/samitolvanen/linux.git x86-cfi-v4 > > I tested this series with near ToT clang with CONFIG_LTO_CLANG_THIN=y > and our small buildroot-based userspace image in QEMU, then again with > CONFIG_LTO_CLANG_FULL=y. No new warnings from objtool, everything > seemed fine. FWIW, > > Tested-by: Nick Desaulniers <ndesaulniers@google.com> >
Hi Sami,
I tested your v4 with a selfmade PGO+ThinlTO optimized LLVM-13 toolchain. And booted on bare metal. My kernel-config is attached.
Thanks.
Regards, - Sedat -
> > > > --- > > Changes in v4: > > - Dropped the extable patch after the code was refactored in -tip. > > > > - Switched to __section() instead of open-coding the attribute. > > > > - Added an explicit ifdef for filtering out CC_FLAGS_CFI in > > purgatory for readability. > > > > - Added a comment to arch_cfi_jump_reloc_offset() in objtool. > > > > Changes in v3: > > - Dropped Clang requirement to >= 13 after the missing compiler > > fix was backported there. > > > > - Added DEFINE_CFI_IMMEDIATE_RETURN_STUB to address the issue > > with tp_stub_func in kernel/tracepoint.c. > > > > - Renamed asm_func_t to asm_func_ptr. > > > > - Changed extable handlers to use __cficanonical instead of > > disabling CFI for fixup_exception. > > > > Changes in v2: > > - Dropped the first objtool patch as the warnings were fixed in > > separate patches. > > > > - Changed fix_cfi_relocs() in objtool to not rely on jump table > > symbols, and to return an error if it can't find a relocation. > > > > - Fixed a build issue with ASM_STACK_FRAME_NON_STANDARD(). > > > > - Dropped workarounds for inline assembly references to > > address-taken static functions with CFI as this was fixed in > > the compiler. > > > > - Changed the C declarations of non-callable functions to use > > opaque types and dropped the function_nocfi() patches. > > > > - Changed ARCH_SUPPORTS_CFI_CLANG to depend on Clang >=14 for > > the compiler fixes. > > > > > > Kees Cook (1): > > x86, relocs: Ignore __typeid__ relocations > > > > Sami Tolvanen (14): > > objtool: Add CONFIG_CFI_CLANG support > > objtool: Add ASM_STACK_FRAME_NON_STANDARD > > linkage: Add DECLARE_ASM_FUNC_SYMBOL > > cfi: Add DEFINE_CFI_IMMEDIATE_RETURN_STUB > > tracepoint: Exclude tp_stub_func from CFI checking > > ftrace: Use an opaque type for functions not callable from C > > lkdtm: Disable UNSET_SMEP with CFI > > lkdtm: Use an opaque type for lkdtm_rodata_do_nothing > > x86: Use an opaque type for functions not callable from C > > x86/purgatory: Disable CFI > > x86, module: Ignore __typeid__ relocations > > x86, cpu: Use LTO for cpu.c with CFI > > x86, kprobes: Fix optprobe_template_func type mismatch > > x86, build: Allow CONFIG_CFI_CLANG to be selected > > > > arch/x86/Kconfig | 1 + > > arch/x86/include/asm/ftrace.h | 2 +- > > arch/x86/include/asm/idtentry.h | 10 +++--- > > arch/x86/include/asm/page_64.h | 7 ++-- > > arch/x86/include/asm/paravirt_types.h | 3 +- > > arch/x86/include/asm/processor.h | 2 +- > > arch/x86/include/asm/proto.h | 25 ++++++------- > > arch/x86/include/asm/uaccess_64.h | 9 ++--- > > arch/x86/kernel/alternative.c | 2 +- > > arch/x86/kernel/ftrace.c | 2 +- > > arch/x86/kernel/kprobes/opt.c | 4 +-- > > arch/x86/kernel/module.c | 4 +++ > > arch/x86/kernel/paravirt.c | 4 +-- > > arch/x86/kvm/emulate.c | 4 +-- > > arch/x86/kvm/kvm_emulate.h | 9 ++--- > > arch/x86/power/Makefile | 2 ++ > > arch/x86/purgatory/Makefile | 4 +++ > > arch/x86/tools/relocs.c | 7 ++++ > > arch/x86/xen/enlighten_pv.c | 6 ++-- > > arch/x86/xen/xen-ops.h | 10 +++--- > > drivers/misc/lkdtm/bugs.c | 2 +- > > drivers/misc/lkdtm/lkdtm.h | 2 +- > > drivers/misc/lkdtm/perms.c | 2 +- > > drivers/misc/lkdtm/rodata.c | 2 +- > > include/asm-generic/vmlinux.lds.h | 11 ++++++ > > include/linux/cfi.h | 13 +++++++ > > include/linux/ftrace.h | 7 ++-- > > include/linux/linkage.h | 13 +++++++ > > include/linux/objtool.h | 6 ++++ > > kernel/cfi.c | 24 ++++++++++++- > > kernel/tracepoint.c | 5 +-- > > tools/include/linux/objtool.h | 6 ++++ > > tools/objtool/arch/x86/decode.c | 17 +++++++++ > > tools/objtool/elf.c | 51 +++++++++++++++++++++++++++ > > tools/objtool/include/objtool/arch.h | 3 ++ > > tools/objtool/include/objtool/elf.h | 2 +- > > 36 files changed, 217 insertions(+), 66 deletions(-) > > > > > > base-commit: d4bfebd9ef497ee0afb498f6028a5074a6ccf307 > > -- > > 2.33.0.800.g4c38ced690-goog > > > > > -- > Thanks, > ~Nick Desaulniers [unhandled content-type:application/octet-stream] | |