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Nick Desaulniers edefb93570 x86/paravirt: Make native_save_fl() extern inline 
commit d0a8d9378d 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.

Debugged-by: Alistair Strachan <astrachan@google.com>
Debugged-by: Matthias Kaehlcke <mka@chromium.org>
Suggested-by: Arnd Bergmann <arnd@arndb.de>
Suggested-by: H. Peter Anvin <hpa@zytor.com>
Suggested-by: Tom Stellar <tstellar@redhat.com>
Reported-by: Sedat Dilek <sedat.dilek@gmail.com>
Tested-by: Sedat Dilek <sedat.dilek@gmail.com>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Acked-by: Juergen Gross <jgross@suse.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: acme@redhat.com
Cc: akataria@vmware.com
Cc: akpm@linux-foundation.org
Cc: andrea.parri@amarulasolutions.com
Cc: ard.biesheuvel@linaro.org
Cc: aryabinin@virtuozzo.com
Cc: astrachan@google.com
Cc: boris.ostrovsky@oracle.com
Cc: brijesh.singh@amd.com
Cc: caoj.fnst@cn.fujitsu.com
Cc: geert@linux-m68k.org
Cc: ghackmann@google.com
Cc: gregkh@linuxfoundation.org
Cc: jan.kiszka@siemens.com
Cc: jarkko.sakkinen@linux.intel.com
Cc: joe@perches.com
Cc: jpoimboe@redhat.com
Cc: keescook@google.com
Cc: kirill.shutemov@linux.intel.com
Cc: kstewart@linuxfoundation.org
Cc: linux-efi@vger.kernel.org
Cc: linux-kbuild@vger.kernel.org
Cc: manojgupta@google.com
Cc: mawilcox@microsoft.com
Cc: michal.lkml@markovi.net
Cc: mjg59@google.com
Cc: mka@chromium.org
Cc: pombredanne@nexb.com
Cc: rientjes@google.com
Cc: rostedt@goodmis.org
Cc: thomas.lendacky@amd.com
Cc: tweek@google.com
Cc: virtualization@lists.linux-foundation.org
Cc: will.deacon@arm.com
Cc: yamada.masahiro@socionext.com
Link: http://lkml.kernel.org/r/20180621162324.36656-4-ndesaulniers@google.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
 		2018-07-22 14:28:42 +02:00
..
alpha locking/xchg/alpha: Fix xchg() and cmpxchg() memory ordering bugs 2018-05-30 07:52:02 +02:00
arc ARC: setup cpu possible mask according to possible-cpus dts property 2018-05-30 07:52:07 +02:00
arm ARM: dts: imx6q: Use correct SDMA script for SPI5 core 2018-07-08 15:30:51 +02:00
arm64 arm64: neon: Fix function may_use_simd() return error status 2018-07-17 11:39:30 +02:00
blackfin pinctrl: adi2: Fix Kconfig build problem 2017-12-20 10:10:34 +01:00
c6x License cleanup: add SPDX license identifier to uapi header files with a license 2017-11-02 11:20:11 +01:00
cris bug.h: work around GCC PR82365 in BUG() 2018-05-30 07:52:00 +02:00
frv License cleanup: add SPDX license identifier to uapi header files with a license 2017-11-02 11:20:11 +01:00
h8300 h8300: remove extraneous __BIG_ENDIAN definition 2018-03-28 18:24:38 +02:00
hexagon hexagon: export csum_partial_copy_nocheck 2018-06-21 04:02:52 +09:00
ia64 ia64/err-inject: Use get_user_pages_fast() 2018-05-30 07:52:11 +02:00
m32r m32r: fix endianness constraints 2018-02-28 10:19:44 +01:00
m68k m68k/mac: Fix SWIM memory resource end address 2018-07-03 11:24:46 +02:00
metag .gitignore: move *.dtb and *.dtb.S patterns to the top-level .gitignore 2018-02-13 10:19:46 +01:00
microblaze microblaze: Setup dependencies for ASM optimized lib functions 2018-04-29 11:33:16 +02:00
mips MIPS: Fix ioremap() RAM check 2018-07-17 11:39:23 +02:00
mn10300 mn10300/misalignment: Use SIGSEGV SEGV_MAPERR to report a failed user copy 2018-02-16 20:23:11 +01:00
nios2 .gitignore: move *.dtb and *.dtb.S patterns to the top-level .gitignore 2018-02-13 10:19:46 +01:00
openrisc kmemcheck: remove annotations 2018-02-22 15:42:23 +01:00
parisc parisc: Move setup_profiling_timer() out of init section 2018-06-21 04:03:01 +09:00
powerpc powerpc/fadump: Unregister fadump on kexec down path. 2018-07-03 11:24:51 +02:00
s390 s390: Correct register corruption in critical section cleanup 2018-07-11 16:29:14 +02:00
score License cleanup: add SPDX license identifier to uapi header files with no license 2017-11-02 11:19:54 +01:00
sh sh: fix build failure for J2 cpu with SMP disabled 2018-06-21 04:02:54 +09:00
sparc sparc64: Make atomic_xchg() an inline function rather than a macro. 2018-05-30 07:52:25 +02:00
tile fcntl: don't cap l_start and l_end values for F_GETLK64 in compat syscall 2017-12-17 15:07:59 +01:00
um um: Use POSIX ucontext_t instead of struct ucontext 2018-04-24 09:36:33 +02:00
unicore32 kmemcheck: stop using GFP_NOTRACK and SLAB_NOTRACK 2018-02-22 15:42:23 +01:00
x86 x86/paravirt: Make native_save_fl() extern inline 2018-07-22 14:28:42 +02:00
xtensa signal/xtensa: Consistenly use SIGBUS in do_unaligned_user 2018-07-03 11:24:47 +02:00
.gitignore
…
Kconfig kprobes: Use synchronize_rcu_tasks() for optprobe with CONFIG_PREEMPT=y 2017-12-10 13:40:40 +01:00