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    SubjectRe: [PATCH v4 11/45] kmsan: add KMSAN runtime core
    On Fri, Jul 01, 2022 at 04:22PM +0200, 'Alexander Potapenko' via kasan-dev wrote:
    [...]
    > diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
    > index 2e24db4bff192..59819e6fa5865 100644
    > --- a/lib/Kconfig.debug
    > +++ b/lib/Kconfig.debug
    > @@ -963,6 +963,7 @@ config DEBUG_STACKOVERFLOW
    >
    > source "lib/Kconfig.kasan"
    > source "lib/Kconfig.kfence"
    > +source "lib/Kconfig.kmsan"
    >
    > endmenu # "Memory Debugging"
    >
    > diff --git a/lib/Kconfig.kmsan b/lib/Kconfig.kmsan
    > new file mode 100644
    > index 0000000000000..8f768d4034e3c
    > --- /dev/null
    > +++ b/lib/Kconfig.kmsan
    > @@ -0,0 +1,50 @@
    > +# SPDX-License-Identifier: GPL-2.0-only
    > +config HAVE_ARCH_KMSAN
    > + bool
    > +
    > +config HAVE_KMSAN_COMPILER
    > + # Clang versions <14.0.0 also support -fsanitize=kernel-memory, but not
    > + # all the features necessary to build the kernel with KMSAN.
    > + depends on CC_IS_CLANG && CLANG_VERSION >= 140000
    > + def_bool $(cc-option,-fsanitize=kernel-memory -mllvm -msan-disable-checks=1)
    > +
    > +config HAVE_KMSAN_PARAM_RETVAL
    > + # Separate check for -fsanitize-memory-param-retval support.

    This comment doesn't add much value, maybe instead say that "Supported
    only by Clang >= 15."

    > + depends on CC_IS_CLANG && CLANG_VERSION >= 140000

    Why not just "depends on HAVE_KMSAN_COMPILER"? (All
    fsanitize-memory-param-retval supporting compilers must also be KMSAN
    compilers.)

    > + def_bool $(cc-option,-fsanitize=kernel-memory -fsanitize-memory-param-retval)
    > +
    > +

    HAVE_KMSAN_PARAM_RETVAL should be moved under "if KMSAN" so that this
    isn't unnecessarily evaluated in every kernel build (saving 1 shelling
    out to clang in most builds).

    > +config KMSAN
    > + bool "KMSAN: detector of uninitialized values use"
    > + depends on HAVE_ARCH_KMSAN && HAVE_KMSAN_COMPILER
    > + depends on SLUB && DEBUG_KERNEL && !KASAN && !KCSAN
    > + select STACKDEPOT
    > + select STACKDEPOT_ALWAYS_INIT
    > + help
    > + KernelMemorySanitizer (KMSAN) is a dynamic detector of uses of
    > + uninitialized values in the kernel. It is based on compiler
    > + instrumentation provided by Clang and thus requires Clang to build.
    > +
    > + An important note is that KMSAN is not intended for production use,
    > + because it drastically increases kernel memory footprint and slows
    > + the whole system down.
    > +
    > + See <file:Documentation/dev-tools/kmsan.rst> for more details.
    > +
    > +if KMSAN
    > +
    > +config KMSAN_CHECK_PARAM_RETVAL
    > + bool "Check for uninitialized values passed to and returned from functions"
    > + default HAVE_KMSAN_PARAM_RETVAL

    This can be enabled even if !HAVE_KMSAN_PARAM_RETVAL. Should this be:

    default y
    depends on HAVE_KMSAN_PARAM_RETVAL

    instead?

    > + help
    > + If the compiler supports -fsanitize-memory-param-retval, KMSAN will
    > + eagerly check every function parameter passed by value and every
    > + function return value.
    > +
    > + Disabling KMSAN_CHECK_PARAM_RETVAL will result in tracking shadow for
    > + function parameters and return values across function borders. This
    > + is a more relaxed mode, but it generates more instrumentation code and
    > + may potentially report errors in corner cases when non-instrumented
    > + functions call instrumented ones.
    > +

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