Greg Kroah-Hartman
2018-Jul-23 12:41 UTC
[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 at google.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 at google.com> Debugged-by: Matthias Kaehlcke <mka at chromium.org> Suggested-by: Arnd Bergmann <arnd at arndb.de> Suggested-by: H. Peter Anvin <hpa at zytor.com> Suggested-by: Tom Stellar <tstellar at redhat.com> Reported-by: Sedat Dilek <sedat.dilek at gmail.com> Tested-by: Sedat Dilek <sedat.dilek at gmail.com> Signed-off-by: Nick Desaulniers <ndesaulniers at google.com> Acked-by: Juergen Gross <jgross at suse.com> Cc: Linus Torvalds <torvalds at linux-foundation.org> Cc: Peter Zijlstra <peterz at infradead.org> Cc: Thomas Gleixner <tglx at linutronix.de> Cc: acme at redhat.com Cc: akataria at vmware.com Cc: akpm at linux-foundation.org Cc: andrea.parri at amarulasolutions.com Cc: ard.biesheuvel at linaro.org Cc: aryabinin at virtuozzo.com Cc: astrachan at google.com Cc: boris.ostrovsky at oracle.com Cc: brijesh.singh at amd.com Cc: caoj.fnst at cn.fujitsu.com Cc: geert at linux-m68k.org Cc: ghackmann at google.com Cc: gregkh at linuxfoundation.org Cc: jan.kiszka at siemens.com Cc: jarkko.sakkinen at linux.intel.com Cc: joe at perches.com Cc: jpoimboe at redhat.com Cc: keescook at google.com Cc: kirill.shutemov at linux.intel.com Cc: kstewart at linuxfoundation.org Cc: linux-efi at vger.kernel.org Cc: linux-kbuild at vger.kernel.org Cc: manojgupta at google.com Cc: mawilcox at microsoft.com Cc: michal.lkml at markovi.net Cc: mjg59 at google.com Cc: mka at chromium.org Cc: pombredanne at nexb.com Cc: rientjes at google.com Cc: rostedt at goodmis.org Cc: thomas.lendacky at amd.com Cc: tweek at google.com Cc: virtualization at lists.linux-foundation.org Cc: will.deacon at arm.com Cc: yamada.masahiro at socionext.com Link: http://lkml.kernel.org/r/20180621162324.36656-4-ndesaulniers at google.com Signed-off-by: Ingo Molnar <mingo at kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.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)
Maybe Matching Threads
- [PATCH 4.17 003/101] x86/paravirt: Make native_save_fl() extern inline
- [PATCH 4.9 07/66] x86/paravirt: Make native_save_fl() extern inline
- [PATCH 4.14 03/92] x86/paravirt: Make native_save_fl() extern inline
- Patch "x86/paravirt: Make native_save_fl() extern inline" has been added to the 4.17-stable tree
- Patch "x86/paravirt: Make native_save_fl() extern inline" has been added to the 4.14-stable tree