Linux/linux c8401dd — arch/x86/include/asm kvm_emulate.h, arch/x86/kvm x86.c emulate.c
KVM: x86: fix singlestepping over syscall
TF is handled a bit differently for syscall and sysret, compared
to the other instructions: TF is checked after the instruction completes,
so that the OS can disable #DB at a syscall by adding TF to FMASK.
When the sysret is executed the #DB is taken "as if" the syscall insn
just completed.
KVM emulates syscall so that it can trap 32-bit syscall on Intel processors.
Fix the behavior, otherwise you could get #DB on a user stack which is not
nice. This does not affect Linux guests, as they use an IST or task gate
for #DB.
This fixes CVE-2017-7518.
Cc: stable at vger.kernel.org
Reported-by: Andy Lutomirski <luto at kernel.org>
Signed-off-by: Paolo Bonzini <pbonzini at redhat.com>
Signed-off-by: Radim Krčmář <rkrcmar at redhat.com>
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