AuxXxilium/linux_dsm_epyc7002
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17be0aec74
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Denys Vlasenko 17be0aec74 x86/asm/entry/64: Implement better check for canonical addresses 
This change makes the check exact (no more false positives
on "negative" addresses).

Andy explains:

 "Canonical addresses either start with 17 zeros or 17 ones.

  In the old code, we checked that the top (64-47) = 17 bits were all
  zero.  We did this by shifting right by 47 bits and making sure that
  nothing was left.

  In the new code, we're shifting left by (64 - 48) = 16 bits and then
  signed shifting right by the same amount, this propagating the 17th
  highest bit to all positions to its left.  If we get the same value we
  started with, then we're good to go."

While it isn't really important to be fully correct here -
almost all addresses we'll ever see will be userspace ones,
but OTOH it looks to be cheap enough: the new code uses
two more ALU ops but preserves %rcx, allowing to not
reload it from pt_regs->cx again.

On disassembly level, the changes are:

  cmp %rcx,0x80(%rsp) -> mov 0x80(%rsp),%r11; cmp %rcx,%r11
  shr $0x2f,%rcx      -> shl $0x10,%rcx; sar $0x10,%rcx; cmp %rcx,%r11
  mov 0x58(%rsp),%rcx -> (eliminated)

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
Acked-by: Andy Lutomirski <luto@kernel.org>
Cc: Alexei Starovoitov <ast@plumgrid.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Drewry <wad@chromium.org>
Link: http://lkml.kernel.org/r/1429633649-20169-1-git-send-email-dvlasenk@redhat.com
[ Changelog massage. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2015-04-22 08:37:56 +02:00
..
boot Merge branch 'x86-boot-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2015-04-13 13:19:10 -07:00
configs
crypto x86/asm: Replace "MOVQ $imm, %reg" with MOVL 2015-04-01 13:17:39 +02:00
ia32 x86, paravirt, xen: Remove the 64-bit ->irq_enable_sysexit() pvop 2015-04-22 08:07:45 +02:00
include x86/asm: Always inline atomics 2015-04-22 08:14:41 +02:00
kernel x86/asm/entry/64: Implement better check for canonical addresses 2015-04-22 08:37:56 +02:00
kvm Merge branch 'timers-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2015-04-13 11:08:28 -07:00
lguest x86/asm/entry/irq: Simplify interrupt dispatch table (IDT) layout 2015-04-08 09:02:13 +02:00
lib Merge branch 'x86-asm-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2015-04-13 13:16:36 -07:00
math-emu
mm Merge branch 'x86-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2015-04-13 13:34:46 -07:00
net
oprofile
pci
platform Merge branch 'x86-platform-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2015-04-13 13:32:35 -07:00
power x86/asm, x86/power/hibernate: Use local labels in asm 2015-04-15 11:37:51 +02:00
purgatory
realmode
syscalls
tools
um
vdso Merge branch 'x86-vdso-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2015-04-13 13:36:45 -07:00
video
xen x86, paravirt, xen: Remove the 64-bit ->irq_enable_sysexit() pvop 2015-04-22 08:07:45 +02:00
.gitignore
Kbuild
Kconfig Merge branch 'x86-mm-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2015-04-13 13:31:32 -07:00
Kconfig.cpu
Kconfig.debug
Makefile
Makefile_32.cpu
Makefile.um