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Message-Id: <20180723122413.797031305@linuxfoundation.org>
Date: Mon, 23 Jul 2018 14:41:12 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-kernel@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
stable@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
"H. Peter Anvin" <hpa@...or.com>,
Tom Stellar <tstellar@...hat.com>,
Sedat Dilek <sedat.dilek@...il.com>,
Nick Desaulniers <ndesaulniers@...gle.com>,
Juergen Gross <jgross@...e.com>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Peter Zijlstra <peterz@...radead.org>,
Thomas Gleixner <tglx@...utronix.de>, acme@...hat.com,
akataria@...are.com, akpm@...ux-foundation.org,
andrea.parri@...rulasolutions.com, ard.biesheuvel@...aro.org,
aryabinin@...tuozzo.com, astrachan@...gle.com,
boris.ostrovsky@...cle.com, brijesh.singh@....com,
caoj.fnst@...fujitsu.com, geert@...ux-m68k.org,
ghackmann@...gle.com, jan.kiszka@...mens.com,
jarkko.sakkinen@...ux.intel.com, joe@...ches.com,
jpoimboe@...hat.com, keescook@...gle.com,
kirill.shutemov@...ux.intel.com, kstewart@...uxfoundation.org,
linux-efi@...r.kernel.org, linux-kbuild@...r.kernel.org,
manojgupta@...gle.com, mawilcox@...rosoft.com,
michal.lkml@...kovi.net, mjg59@...gle.com, mka@...omium.org,
pombredanne@...b.com, rientjes@...gle.com, rostedt@...dmis.org,
thomas.lendacky@....com, tweek@...gle.com,
virtualization@...ts.linux-foundation.org, will.deacon@....com,
yamada.masahiro@...ionext.com, Ingo Molnar <mingo@...nel.org>
Subject: [PATCH 4.4 018/107] x86/paravirt: Make native_save_fl() extern inline
4.4-stable review patch. If anyone has any objections, please let me know.
------------------
From: Nick Desaulniers <ndesaulniers@...gle.com>
commit d0a8d9378d16eb3c69bd8e6d23779fbdbee3a8c7 upstream.
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.
[Backport for 4.4. 4.4 is missing commit 784d5699eddc "x86: move exports to
actual definitions" which doesn't apply cleanly, and not really worth
backporting IMO. It's simpler to change this patch from upstream:
+ #include <asm-generic/export.h>
rather than
+ #include <asm/export.h>]
Debugged-by: Alistair Strachan <astrachan@...gle.com>
Debugged-by: Matthias Kaehlcke <mka@...omium.org>
Suggested-by: Arnd Bergmann <arnd@...db.de>
Suggested-by: H. Peter Anvin <hpa@...or.com>
Suggested-by: Tom Stellar <tstellar@...hat.com>
Reported-by: Sedat Dilek <sedat.dilek@...il.com>
Tested-by: Sedat Dilek <sedat.dilek@...il.com>
Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
Acked-by: Juergen Gross <jgross@...e.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: acme@...hat.com
Cc: akataria@...are.com
Cc: akpm@...ux-foundation.org
Cc: andrea.parri@...rulasolutions.com
Cc: ard.biesheuvel@...aro.org
Cc: aryabinin@...tuozzo.com
Cc: astrachan@...gle.com
Cc: boris.ostrovsky@...cle.com
Cc: brijesh.singh@....com
Cc: caoj.fnst@...fujitsu.com
Cc: geert@...ux-m68k.org
Cc: ghackmann@...gle.com
Cc: gregkh@...uxfoundation.org
Cc: jan.kiszka@...mens.com
Cc: jarkko.sakkinen@...ux.intel.com
Cc: joe@...ches.com
Cc: jpoimboe@...hat.com
Cc: keescook@...gle.com
Cc: kirill.shutemov@...ux.intel.com
Cc: kstewart@...uxfoundation.org
Cc: linux-efi@...r.kernel.org
Cc: linux-kbuild@...r.kernel.org
Cc: manojgupta@...gle.com
Cc: mawilcox@...rosoft.com
Cc: michal.lkml@...kovi.net
Cc: mjg59@...gle.com
Cc: mka@...omium.org
Cc: pombredanne@...b.com
Cc: rientjes@...gle.com
Cc: rostedt@...dmis.org
Cc: thomas.lendacky@....com
Cc: tweek@...gle.com
Cc: virtualization@...ts.linux-foundation.org
Cc: will.deacon@....com
Cc: yamada.masahiro@...ionext.com
Link: http://lkml.kernel.org/r/20180621162324.36656-4-ndesaulniers@google.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
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(-)
--- a/arch/x86/include/asm/irqflags.h
+++ b/arch/x86/include/asm/irqflags.h
@@ -8,7 +8,7 @@
* Interrupt control:
*/
-static inline unsigned long native_save_fl(void)
+extern inline unsigned long native_save_fl(void)
{
unsigned long flags;
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -41,6 +41,7 @@ obj-y += alternative.o i8253.o pci-nom
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/
--- /dev/null
+++ b/arch/x86/kernel/irqflags.S
@@ -0,0 +1,26 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#include <asm/asm.h>
+#include <asm-generic/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)
+ * %eax/%rdi: flags
+ */
+ENTRY(native_restore_fl)
+ push %_ASM_ARG1
+ popf
+ ret
+ENDPROC(native_restore_fl)
+EXPORT_SYMBOL(native_restore_fl)
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