4.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> 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@xxxxxxxxxx> Debugged-by: Matthias Kaehlcke <mka@xxxxxxxxxxxx> Suggested-by: Arnd Bergmann <arnd@xxxxxxxx> Suggested-by: H. Peter Anvin <hpa@xxxxxxxxx> Suggested-by: Tom Stellar <tstellar@xxxxxxxxxx> Reported-by: Sedat Dilek <sedat.dilek@xxxxxxxxx> Tested-by: Sedat Dilek <sedat.dilek@xxxxxxxxx> Signed-off-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> Acked-by: Juergen Gross <jgross@xxxxxxxx> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: acme@xxxxxxxxxx Cc: akataria@xxxxxxxxxx Cc: akpm@xxxxxxxxxxxxxxxxxxxx Cc: andrea.parri@xxxxxxxxxxxxxxxxxxxx Cc: ard.biesheuvel@xxxxxxxxxx Cc: aryabinin@xxxxxxxxxxxxx Cc: astrachan@xxxxxxxxxx Cc: boris.ostrovsky@xxxxxxxxxx Cc: brijesh.singh@xxxxxxx Cc: caoj.fnst@xxxxxxxxxxxxxx Cc: geert@xxxxxxxxxxxxxx Cc: ghackmann@xxxxxxxxxx Cc: gregkh@xxxxxxxxxxxxxxxxxxx Cc: jan.kiszka@xxxxxxxxxxx Cc: jarkko.sakkinen@xxxxxxxxxxxxxxx Cc: joe@xxxxxxxxxxx Cc: jpoimboe@xxxxxxxxxx Cc: keescook@xxxxxxxxxx Cc: kirill.shutemov@xxxxxxxxxxxxxxx Cc: kstewart@xxxxxxxxxxxxxxxxxxx Cc: linux-efi@xxxxxxxxxxxxxxx Cc: linux-kbuild@xxxxxxxxxxxxxxx Cc: manojgupta@xxxxxxxxxx Cc: mawilcox@xxxxxxxxxxxxx Cc: michal.lkml@xxxxxxxxxxx Cc: mjg59@xxxxxxxxxx Cc: mka@xxxxxxxxxxxx Cc: pombredanne@xxxxxxxx Cc: rientjes@xxxxxxxxxx Cc: rostedt@xxxxxxxxxxx Cc: thomas.lendacky@xxxxxxx Cc: tweek@xxxxxxxxxx Cc: virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx Cc: will.deacon@xxxxxxx Cc: yamada.masahiro@xxxxxxxxxxxxx Link: http://lkml.kernel.org/r/20180621162324.36656-4-ndesaulniers@xxxxxxxxxx Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- 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)
