linux-kernel - Reference to non-existing config X86_SMAP in config UBSAN

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Date:   Wed, 1 Jun 2022 12:50:47 +0200
From:   Lukas Bulwahn <lukas.bulwahn@...il.com>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     Borislav Petkov <bp@...e.de>,
        Peter Zijlstra <peterz@...radead.org>,
        kernel-janitors <kernel-janitors@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Reference to non-existing config X86_SMAP in config UBSAN_UNREACHABLE

Dear Josh,

Commit dbae0a934f09 ("x86/cpu: Remove CONFIG_X86_SMAP and "nosmap"")
from Borislav removes the config X86_SMAP and makes smap on x86
default.

Josh, your commit 03f16cd020eb ("objtool: Add CONFIG_OBJTOOL") makes
config UBSAN_UNREACHABLE in lib/Kconfig.ubsan refer to this
non-existing config X86_SMAP.

See this hunk in lib/Kconfig.ubsan:

diff --git a/lib/Kconfig.ubsan b/lib/Kconfig.ubsan
index f3c57ed51838..c4fe15d38b60 100644
--- a/lib/Kconfig.ubsan
+++ b/lib/Kconfig.ubsan
@@ -94,7 +94,7 @@ config UBSAN_UNREACHABLE
        bool "Perform checking for unreachable code"
        # objtool already handles unreachable checking and gets angry about
        # seeing UBSan instrumentation located in unreachable places.
-       depends on !STACK_VALIDATION
+       depends on !(OBJTOOL && (STACK_VALIDATION || UNWINDER_ORC || X86_SMAP))
        depends on $(cc-option,-fsanitize=unreachable)
        help
          This option enables -fsanitize=unreachable which checks for control

I think X86_SMAP can just be dropped in this line, but I leave it up
to you to change, as I am not completely certain on the needed change
and if that just breaks the config dependencies for stack validation.

By the way, this issue was identified with the script
./scripts/checkkconfigsymbols.py

Best regards,

Lukas