linux-kernel - [PATCH 5/9] Add RUNTIME_DISCARD

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Date:   Thu, 27 Feb 2020 16:22:40 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Borislav Petkov <bp@...e.de>
Cc:     Kees Cook <keescook@...omium.org>, "H.J. Lu" <hjl.tools@...il.com>,
        Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Peter Collingbourne <pcc@...gle.com>,
        James Morse <james.morse@....com>,
        Arnd Bergmann <arnd@...db.de>,
        Masahiro Yamada <masahiroy@...nel.org>, x86@...nel.org,
        linux-arm-kernel@...ts.infradead.org, linux-arch@...r.kernel.org,
        linux-kbuild@...r.kernel.org, clang-built-linux@...glegroups.com,
        linux-kernel@...r.kernel.org
Subject: [PATCH 5/9] Add RUNTIME_DISCARD_EXIT to generic DISCARDS

From: "H.J. Lu" <hjl.tools@...il.com>

In x86 kernel, .exit.text and .exit.data sections are discarded at
runtime, not by linker.  Add RUNTIME_DISCARD_EXIT to generic DISCARDS
and define it in x86 kernel linker script to keep them.

Signed-off-by: H.J. Lu <hjl.tools@...il.com>
Link: https://lore.kernel.org/r/20200130224337.4150-1-hjl.tools@gmail.com
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 arch/x86/kernel/vmlinux.lds.S     |  1 +
 include/asm-generic/vmlinux.lds.h | 10 ++++++++--
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index 1e345f302a46..1e12c097d09b 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -21,6 +21,7 @@
 #define LOAD_OFFSET __START_KERNEL_map
 #endif
 
+#define RUNTIME_DISCARD_EXIT
 #define EMITS_PT_NOTE
 #define RO_EXCEPTION_TABLE_ALIGN	16
 
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 303597e51396..1797f2c9bb41 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -894,10 +894,16 @@
  * section definitions so that such archs put those in earlier section
  * definitions.
  */
+#ifdef RUNTIME_DISCARD_EXIT
+#define EXIT_DISCARDS
+#else
+#define EXIT_DISCARDS							\
+	EXIT_TEXT							\
+	EXIT_DATA
+#endif
 #define DISCARDS							\
 	/DISCARD/ : {							\
-	EXIT_TEXT							\
-	EXIT_DATA							\
+	EXIT_DISCARDS							\
 	EXIT_CALL							\
 	*(.discard)							\
 	*(.discard.*)							\
-- 
2.20.1