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    Subject[PATCH 5.19 255/365] x86/ibt, objtool: Add IBT_NOSEAL()
    Date
    From: Josh Poimboeuf <jpoimboe@kernel.org>

    [ Upstream commit e27e5bea956ce4d3eb15112de5fa5a3b77c2f488 ]

    Add a macro which prevents a function from getting sealed if there are
    no compile-time references to it.

    Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
    Message-Id: <20220818213927.e44fmxkoq4yj6ybn@treble>
    Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    arch/x86/include/asm/ibt.h | 11 +++++++++++
    tools/objtool/check.c | 3 ++-
    2 files changed, 13 insertions(+), 1 deletion(-)

    diff --git a/arch/x86/include/asm/ibt.h b/arch/x86/include/asm/ibt.h
    index 689880eca9ba..9b08082a5d9f 100644
    --- a/arch/x86/include/asm/ibt.h
    +++ b/arch/x86/include/asm/ibt.h
    @@ -31,6 +31,16 @@

    #define __noendbr __attribute__((nocf_check))

    +/*
    + * Create a dummy function pointer reference to prevent objtool from marking
    + * the function as needing to be "sealed" (i.e. ENDBR converted to NOP by
    + * apply_ibt_endbr()).
    + */
    +#define IBT_NOSEAL(fname) \
    + ".pushsection .discard.ibt_endbr_noseal\n\t" \
    + _ASM_PTR fname "\n\t" \
    + ".popsection\n\t"
    +
    static inline __attribute_const__ u32 gen_endbr(void)
    {
    u32 endbr;
    @@ -84,6 +94,7 @@ extern __noendbr void ibt_restore(u64 save);
    #ifndef __ASSEMBLY__

    #define ASM_ENDBR
    +#define IBT_NOSEAL(name)

    #define __noendbr

    diff --git a/tools/objtool/check.c b/tools/objtool/check.c
    index b341f8a8c7c5..31c719f99f66 100644
    --- a/tools/objtool/check.c
    +++ b/tools/objtool/check.c
    @@ -4096,7 +4096,8 @@ static int validate_ibt(struct objtool_file *file)
    * These sections can reference text addresses, but not with
    * the intent to indirect branch to them.
    */
    - if (!strncmp(sec->name, ".discard", 8) ||
    + if ((!strncmp(sec->name, ".discard", 8) &&
    + strcmp(sec->name, ".discard.ibt_endbr_noseal")) ||
    !strncmp(sec->name, ".debug", 6) ||
    !strcmp(sec->name, ".altinstructions") ||
    !strcmp(sec->name, ".ibt_endbr_seal") ||
    --
    2.35.1


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