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    Subject[PATCH V3 1/7] x86/entry: Introduce __entry_text for entry code written in C
    Date
    From: Lai Jiangshan <jiangshan.ljs@antgroup.com>

    Some entry code will be implemented in C files.
    Introduce __entry_text to set them in .entry.text section.

    The new __entry_text disables instrumentation like noinstr, so
    __noinstr_section() is added for noinstr and the new __entry_text.

    Note, entry code can not access to %gs before the %gs base is switched
    to kernel %gs base, so stack protector can not be used on the C entry
    code. But __entry_text doesn't disable stack protector since some
    compilers might not support function level granular attribute to
    disable stack protector. It will be disabled in C file level.

    Cc: Borislav Petkov <bp@alien8.de>
    Reviewed-by: Miguel Ojeda <ojeda@kernel.org>
    Reviewed-by: Kees Cook <keescook@chromium.org>
    Suggested-by: Nick Desaulniers <ndesaulniers@google.com>
    Suggested-by: Peter Zijlstra <peterz@infradead.org>
    Signed-off-by: Lai Jiangshan <jiangshan.ljs@antgroup.com>
    ---
    arch/x86/include/asm/idtentry.h | 3 +++
    include/linux/compiler_types.h | 8 +++++---
    2 files changed, 8 insertions(+), 3 deletions(-)

    diff --git a/arch/x86/include/asm/idtentry.h b/arch/x86/include/asm/idtentry.h
    index 72184b0b2219..acc4c99f801c 100644
    --- a/arch/x86/include/asm/idtentry.h
    +++ b/arch/x86/include/asm/idtentry.h
    @@ -13,6 +13,9 @@

    #include <asm/irq_stack.h>

    +/* Entry code written in C. */
    +#define __entry_text __noinstr_section(".entry.text")
    +
    /**
    * DECLARE_IDTENTRY - Declare functions for simple IDT entry points
    * No error code pushed by hardware
    diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
    index d08dfcb0ac68..bd9d9d19dc9b 100644
    --- a/include/linux/compiler_types.h
    +++ b/include/linux/compiler_types.h
    @@ -225,9 +225,11 @@ struct ftrace_likely_data {
    #endif

    /* Section for code which can't be instrumented at all */
    -#define noinstr \
    - noinline notrace __attribute((__section__(".noinstr.text"))) \
    - __no_kcsan __no_sanitize_address __no_profile __no_sanitize_coverage
    +#define __noinstr_section(section) \
    + noinline notrace __section(section) __no_kcsan \
    + __no_sanitize_address __no_profile __no_sanitize_coverage
    +
    +#define noinstr __noinstr_section(".noinstr.text")

    #endif /* __KERNEL__ */

    --
    2.19.1.6.gb485710b
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