On Mon, Feb 03, 2020 at 11:16:05PM +0800, Xiaoyao Li wrote: > If split lock detect is enabled (warn/fatal), #AC handler calls die() > when split lock happens in kernel. > > A sane guest should never tigger emulation on a split-lock access, but > it cannot prevent malicous guest from doing this. So just emulating the > access as a write if it's a split-lock access to avoid malicous guest > polluting the kernel log. > > More detail analysis can be found: > https://lkml.kernel.org/r/20200131200134.GD18946@xxxxxxxxxxxxxxx > > Signed-off-by: Xiaoyao Li <xiaoyao.li@xxxxxxxxx> > --- > arch/x86/kvm/x86.c | 11 +++++++++++ > 1 file changed, 11 insertions(+) > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 2d3be7f3ad67..821b7404c0fd 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -5847,6 +5847,13 @@ static int emulator_write_emulated(struct x86_emulate_ctxt *ctxt, > (cmpxchg64((u64 *)(ptr), *(u64 *)(old), *(u64 *)(new)) == *(u64 *)(old)) > #endif > > +static inline bool across_cache_line_access(gpa_t gpa, unsigned int bytes) s/across/split so as not to introduce another name. > +{ > + unsigned int cache_line_size = cache_line_size(); > + > + return (gpa & (cache_line_size - 1)) + bytes > cache_line_size; I'd prefer to use the same logic as the page-split to avoid having to reason about the correctness of two different algorithms. > +} > + > static int emulator_cmpxchg_emulated(struct x86_emulate_ctxt *ctxt, > unsigned long addr, > const void *old, > @@ -5873,6 +5880,10 @@ static int emulator_cmpxchg_emulated(struct x86_emulate_ctxt *ctxt, > if (((gpa + bytes - 1) & PAGE_MASK) != (gpa & PAGE_MASK)) > goto emul_write; > > + if (get_split_lock_detect_state() != sld_off && > + across_cache_line_access(gpa, bytes)) > + goto emul_write; As an alternative to the above, the page/line splits can be handled in a single check, e.g. page_line_mask = PAGE_MASK; if (is_split_lock_detect_enabled()) page_line_mask = cache_line_size() - 1; if (((gpa + bytes - 1) & page_line_mask) != (gpa & page_line_mask)) goto emul_write; > + > if (kvm_vcpu_map(vcpu, gpa_to_gfn(gpa), &map)) > goto emul_write; > > -- > 2.23.0 >
