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mirror of https://github.com/edk2-porting/linux-next.git synced 2024-12-23 12:43:55 +08:00
linux-next/arch/x86
Alexander Potapenko 5b77e95dd7 x86/asm: Use stricter assembly constraints in bitops
There's a number of problems with how arch/x86/include/asm/bitops.h
is currently using assembly constraints for the memory region
bitops are modifying:

1) Use memory clobber in bitops that touch arbitrary memory

Certain bit operations that read/write bits take a base pointer and an
arbitrarily large offset to address the bit relative to that base.
Inline assembly constraints aren't expressive enough to tell the
compiler that the assembly directive is going to touch a specific memory
location of unknown size, therefore we have to use the "memory" clobber
to indicate that the assembly is going to access memory locations other
than those listed in the inputs/outputs.

To indicate that BTR/BTS instructions don't necessarily touch the first
sizeof(long) bytes of the argument, we also move the address to assembly
inputs.

This particular change leads to size increase of 124 kernel functions in
a defconfig build. For some of them the diff is in NOP operations, other
end up re-reading values from memory and may potentially slow down the
execution. But without these clobbers the compiler is free to cache
the contents of the bitmaps and use them as if they weren't changed by
the inline assembly.

2) Use byte-sized arguments for operations touching single bytes.

Passing a long value to ANDB/ORB/XORB instructions makes the compiler
treat sizeof(long) bytes as being clobbered, which isn't the case. This
may theoretically lead to worse code in the case of heavy optimization.

Practical impact:

I've built a defconfig kernel and looked through some of the functions
generated by GCC 7.3.0 with and without this clobber, and didn't spot
any miscompilations.

However there is a (trivial) theoretical case where this code leads to
miscompilation:

  https://lkml.org/lkml/2019/3/28/393

using just GCC 8.3.0 with -O2.  It isn't hard to imagine someone writes
such a function in the kernel someday.

So the primary motivation is to fix an existing misuse of the asm
directive, which happens to work in certain configurations now, but
isn't guaranteed to work under different circumstances.

[ --mingo: Added -stable tag because defconfig only builds a fraction
  of the kernel and the trivial testcase looks normal enough to
  be used in existing or in-development code. ]

Signed-off-by: Alexander Potapenko <glider@google.com>
Cc: <stable@vger.kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: James Y Knight <jyknight@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20190402112813.193378-1-glider@google.com
[ Edited the changelog, tidied up one of the defines. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2019-04-06 09:52:02 +02:00
..
boot x86/boot: Fix incorrect ifdeffery scope 2019-03-27 14:00:51 +01:00
configs Merge branch 'akpm' (patches from Andrew) 2019-03-07 19:25:37 -08:00
crypto crypto: x86/poly1305 - Clear key material from stack in SSE2 variant 2019-02-28 14:17:59 +08:00
entry pidfd patches for v5.1-rc1 2019-03-16 13:47:14 -07:00
events perf/x86/intel: Make dev_attr_allow_tsx_force_abort static 2019-03-17 08:40:18 +01:00
hyperv x86/hyperv: Prevent potential NULL pointer dereference 2019-03-21 12:24:39 +01:00
ia32 a.out: remove core dumping support 2019-03-05 10:00:35 -08:00
include x86/asm: Use stricter assembly constraints in bitops 2019-04-06 09:52:02 +02:00
kernel x86/resctrl: Fix typos in the mba_sc mount option 2019-04-01 18:45:27 +02:00
kvm ARM: some cleanups, direct physical timer assignment, cache sanitization 2019-03-15 15:00:28 -07:00
lib x86/lib: Fix indentation issue, remove extra tab 2019-03-21 12:24:38 +01:00
math-emu Remove 'type' argument from access_ok() function 2019-01-03 18:57:57 -08:00
mm x86/mm: Don't exceed the valid physical address space 2019-03-28 14:13:51 +01:00
net x32: bpf: implement jitting of JMP32 2019-01-26 13:33:02 -08:00
oprofile
pci x86/PCI: Fixup RTIT_BAR of Intel Denverton Trace Hub 2019-02-07 08:43:58 -06:00
platform x86/realmode: Make set_real_mode_mem() static inline 2019-03-29 10:16:27 +01:00
power mm: remove include/linux/bootmem.h 2018-10-31 08:54:16 -07:00
purgatory
ras
realmode x86/realmode: Make set_real_mode_mem() static inline 2019-03-29 10:16:27 +01:00
tools x86: Clean up 'sizeof x' => 'sizeof(x)' 2018-10-29 07:13:28 +01:00
um Merge branch 'timers-2038-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2019-03-05 14:08:26 -08:00
video
xen Merge branch 'akpm' (patches from Andrew) 2019-03-12 10:39:53 -07:00
.gitignore
Kbuild KVM: x86: Allow Qemu/KVM to use PVH entry point 2018-12-13 13:41:49 -05:00
Kconfig DMA mapping updates for 5.1 2019-03-10 11:54:48 -07:00
Kconfig.cpu x86/cpu: Create Hygon Dhyana architecture support file 2018-09-27 16:14:05 +02:00
Kconfig.debug efi/x86: Convert x86 EFI earlyprintk into generic earlycon implementation 2019-02-04 08:27:30 +01:00
Makefile x86/retpolines: Disable switch jump tables when retpolines are enabled 2019-03-28 13:39:48 +01:00
Makefile_32.cpu
Makefile.um x86, powerpc: Remove -funit-at-a-time compiler option entirely 2018-12-09 11:55:32 +01:00