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Message-Id: <20180601165550.90053-4-ndesaulniers@google.com>
Date: Fri, 1 Jun 2018 09:55:50 -0700
From: Nick Desaulniers <ndesaulniers@...gle.com>
To: akpm@...ux-foundation.org, ard.biesheuvel@...aro.org,
aryabinin@...tuozzo.com, akataria@...are.com,
boris.ostrovsky@...cle.com, brijesh.singh@....com,
caoj.fnst@...fujitsu.com, gregkh@...uxfoundation.org,
hpa@...or.com, jan.kiszka@...mens.com,
jarkko.sakkinen@...ux.intel.com, jgross@...e.com,
jpoimboe@...hat.com, kirill.shutemov@...ux.intel.com,
mingo@...hat.com, mjg59@...gle.com, mka@...omium.org,
ndesaulniers@...gle.com, pombredanne@...b.com, rostedt@...dmis.org,
tglx@...utronix.de, thomas.lendacky@....com, tweek@...gle.com
Cc: linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org,
x86@...nel.org, virtualization@...ts.linux-foundation.org
Subject: [PATCH 3/3] x86: paravirt: make native_save_fl extern inline
native_save_fl() is marked static inline, but by using it as
a function pointer in arch/x86/kernel/paravirt.c, it MUST be outlined.
paravirt's use of native_save_fl() also requires that no GPRs other than
%rax are clobbered.
Compilers have different heuristics which they use to emit stack guard
code, the emittance of which can break paravirt's callee saved assumption
by clobbering %rcx.
Marking a function definition extern inline means that if this version
cannot be inlined, then the out-of-line version will be preferred. By
having the out-of-line version be implemented in assembly, it cannot be
instrumented with a stack protector, which might violate custom calling
conventions that code like paravirt rely on.
The semantics of extern inline has changed since gnu89. This means that
folks using GCC versions >= 5.1 may see symbol redefinition errors at
link time for subdirs that override KBUILD_CFLAGS (making the C standard
used implicit) regardless of this patch. This has been cleaned up
earlier in the patch set, but is left as a note in the commit message
for future travelers.
Reports:
https://lkml.org/lkml/2018/5/7/534
https://github.com/ClangBuiltLinux/linux/issues/16
Discussion:
https://bugs.llvm.org/show_bug.cgi?id=37512
https://lkml.org/lkml/2018/5/24/1371
Thanks to the many folks that participated in the discussion.
Debugged-by: Alistair Strachan <astrachan@...gle.com>
Debugged-by: Matthias Kaehlcke <mka@...omium.org>
Reported-by: Sedat Dilek <sedat.dilek@...il.com>
Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
Suggested-by: H. Peter Anvin <hpa@...or.com>
Suggested-by: Tom Stellar <tstellar@...hat.com>
Tested-by: Sedat Dilek <sedat.dilek@...il.com>
---
arch/x86/include/asm/irqflags.h | 2 +-
arch/x86/kernel/Makefile | 1 +
arch/x86/kernel/irqflags.S | 26 ++++++++++++++++++++++++++
3 files changed, 28 insertions(+), 1 deletion(-)
create mode 100644 arch/x86/kernel/irqflags.S
diff --git a/arch/x86/include/asm/irqflags.h b/arch/x86/include/asm/irqflags.h
index 89f08955fff7..c4fc17220df9 100644
--- a/arch/x86/include/asm/irqflags.h
+++ b/arch/x86/include/asm/irqflags.h
@@ -13,7 +13,7 @@
* Interrupt control:
*/
-static inline unsigned long native_save_fl(void)
+extern inline unsigned long native_save_fl(void)
{
unsigned long flags;
diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index 02d6f5cf4e70..8824d01c0c35 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -61,6 +61,7 @@ obj-y += alternative.o i8253.o hw_breakpoint.o
obj-y += tsc.o tsc_msr.o io_delay.o rtc.o
obj-y += pci-iommu_table.o
obj-y += resource.o
+obj-y += irqflags.o
obj-y += process.o
obj-y += fpu/
diff --git a/arch/x86/kernel/irqflags.S b/arch/x86/kernel/irqflags.S
new file mode 100644
index 000000000000..937bd08c3f79
--- /dev/null
+++ b/arch/x86/kernel/irqflags.S
@@ -0,0 +1,26 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#include <asm/asm.h>
+#include <asm/export.h>
+#include <linux/linkage.h>
+
+/*
+ * unsigned long native_save_fl(void)
+ */
+ENTRY(native_save_fl)
+ pushf
+ pop %_ASM_AX
+ ret
+ENDPROC(native_save_fl)
+EXPORT_SYMBOL(native_save_fl)
+
+/*
+ * void native_restore_fl(unsigned long flags)
+ * %rdi: flags
+ */
+ENTRY(native_restore_fl)
+ push %_ASM_DI
+ popf
+ ret
+ENDPROC(native_restore_fl)
+EXPORT_SYMBOL(native_restore_fl)
--
2.17.0.921.gf22659ad46-goog
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