linux-hardening - [PATCH 08/15] x86/extable: Do not mark exception callback as CFI

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Date:   Fri, 16 Apr 2021 13:38:37 -0700
From:   Sami Tolvanen <samitolvanen@...gle.com>
To:     x86@...nel.org
Cc:     Kees Cook <keescook@...omium.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Sedat Dilek <sedat.dilek@...il.com>,
        linux-hardening@...r.kernel.org, linux-kernel@...r.kernel.org,
        clang-built-linux@...glegroups.com,
        Sami Tolvanen <samitolvanen@...gle.com>
Subject: [PATCH 08/15] x86/extable: Do not mark exception callback as CFI

From: Kees Cook <keescook@...omium.org>

The exception table entries are constructed out of a relative offset
and point to the actual function, not the CFI table entry. For now,
just mark the caller as not checking CFI. The failure is most visible
at boot with CONFIG_DEBUG_RODATA_TEST=y.

Signed-off-by: Kees Cook <keescook@...omium.org>
Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>
---
 arch/x86/mm/extable.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/x86/mm/extable.c b/arch/x86/mm/extable.c
index b93d6cd08a7f..a7eae1c4c59f 100644
--- a/arch/x86/mm/extable.c
+++ b/arch/x86/mm/extable.c
@@ -155,6 +155,7 @@ enum handler_type ex_get_fault_handler_type(unsigned long ip)
 		return EX_HANDLER_OTHER;
 }
 
+__nocfi
 int fixup_exception(struct pt_regs *regs, int trapnr, unsigned long error_code,
 		    unsigned long fault_addr)
 {
-- 
2.31.1.368.gbe11c130af-goog