linux/arch
Wanpeng Li 6c86eedc20 KVM: X86: Add Force Emulation Prefix for "emulate the next instruction"
There is no easy way to force KVM to run an instruction through the emulator
(by design as that will expose the x86 emulator as a significant attack-surface).
However, we do wish to expose the x86 emulator in case we are testing it
(e.g. via kvm-unit-tests). Therefore, this patch adds a "force emulation prefix"
that is designed to raise #UD which KVM will trap and it's #UD exit-handler will
match "force emulation prefix" to run instruction after prefix by the x86 emulator.
To not expose the x86 emulator by default, we add a module parameter that should
be off by default.

A simple testcase here:

    #include <stdio.h>
    #include <string.h>

    #define HYPERVISOR_INFO 0x40000000

    #define CPUID(idx, eax, ebx, ecx, edx) \
        asm volatile (\
        "ud2a; .ascii \"kvm\"; cpuid" \
        :"=b" (*ebx), "=a" (*eax), "=c" (*ecx), "=d" (*edx) \
            :"0"(idx) );

    void main()
    {
        unsigned int eax, ebx, ecx, edx;
        char string[13];

        CPUID(HYPERVISOR_INFO, &eax, &ebx, &ecx, &edx);
        *(unsigned int *)(string + 0) = ebx;
        *(unsigned int *)(string + 4) = ecx;
        *(unsigned int *)(string + 8) = edx;

        string[12] = 0;
        if (strncmp(string, "KVMKVMKVM\0\0\0", 12) == 0)
            printf("kvm guest\n");
        else
            printf("bare hardware\n");
    }

Suggested-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Radim Krčmář <rkrcmar@redhat.com>
Reviewed-by: Liran Alon <liran.alon@oracle.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Liran Alon <liran.alon@oracle.com>
Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
[Correctly handle usermode exits. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2018-04-04 19:09:40 +02:00
..
alpha locking/xchg/alpha: Fix xchg() and cmpxchg() memory ordering bugs 2018-02-23 08:38:16 +01:00
arc ARC fixes for 4.16-rc4 2018-03-01 14:32:23 -08:00
arm KVM/ARM updates for v4.17 2018-03-28 16:09:09 +02:00
arm64 KVM/ARM updates for v4.17 2018-03-28 16:09:09 +02:00
blackfin unify {de,}mangle_poll(), get rid of kernel-side POLL... 2018-02-11 14:37:22 -08:00
c6x The core framework has a handful of patches this time around, mostly due 2018-02-01 16:56:07 -08:00
cris bug.h: work around GCC PR82365 in BUG() 2018-02-21 15:35:43 -08:00
frv unify {de,}mangle_poll(), get rid of kernel-side POLL... 2018-02-11 14:37:22 -08:00
h8300 The core framework has a handful of patches this time around, mostly due 2018-02-01 16:56:07 -08:00
hexagon The core framework has a handful of patches this time around, mostly due 2018-02-01 16:56:07 -08:00
ia64 bug.h: work around GCC PR82365 in BUG() 2018-02-21 15:35:43 -08:00
m32r The core framework has a handful of patches this time around, mostly due 2018-02-01 16:56:07 -08:00
m68k bug.h: work around GCC PR82365 in BUG() 2018-02-21 15:35:43 -08:00
metag The core framework has a handful of patches this time around, mostly due 2018-02-01 16:56:07 -08:00
microblaze Microblaze patches for 4.16-rc1 2018-02-02 09:48:36 -08:00
mips KVM: Introduce paravirtualization hints and KVM_HINTS_DEDICATED 2018-03-06 18:40:44 +01:00
mn10300 The core framework has a handful of patches this time around, mostly due 2018-02-01 16:56:07 -08:00
nios2 nios2 update for v4.16-rc1 2018-02-11 13:52:32 -08:00
openrisc The core framework has a handful of patches this time around, mostly due 2018-02-01 16:56:07 -08:00
parisc Merge branch 'parisc-4.16-1' of git://git.kernel.org/pub/scm/linux/kernel/git/deller/parisc-linux 2018-03-02 13:05:20 -08:00
powerpc KVM PPC update for 4.17 2018-03-29 20:20:13 +02:00
riscv riscv/barrier: Define __smp_{mb,rmb,wmb} 2018-02-26 08:44:50 -08:00
s390 KVM: s390: fixes and features 2018-03-16 22:03:18 +01:00
score arch/score/kernel/setup.c: combine two seq_printf() calls into one call in show_cpuinfo() 2018-02-06 18:32:47 -08:00
sh sh: fix build error for empty CONFIG_BUILTIN_DTB_SOURCE 2018-03-02 09:20:55 +09:00
sparc bug.h: work around GCC PR82365 in BUG() 2018-02-21 15:35:43 -08:00
tile The core framework has a handful of patches this time around, mostly due 2018-02-01 16:56:07 -08:00
um mconsole_proc(): don't mess with file->f_pos 2018-02-09 19:28:01 -08:00
unicore32 lib: optimize cpumask_next_and() 2018-02-06 18:32:44 -08:00
x86 KVM: X86: Add Force Emulation Prefix for "emulate the next instruction" 2018-04-04 19:09:40 +02:00
xtensa xtensa: support DMA buffers in high memory 2018-02-16 19:19:54 -08:00
.gitignore
Kconfig Makefile: introduce CONFIG_CC_STACKPROTECTOR_AUTO 2018-02-06 18:32:44 -08:00