Messages in this thread | | | From | Vitaly Kuznetsov <> | Subject | Re: [PATCH 1/4] KVM: x86: Grab regs_dirty in local 'unsigned long' | Date | Thu, 26 May 2022 16:04:37 +0200 |
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Sean Christopherson <seanjc@google.com> writes:
> Capture ctxt->regs_dirty in a local 'unsigned long' instead of casting > ctxt->regs_dirty to an 'unsigned long *' for use in for_each_set_bit(). > The bitops helpers really do read the entire 'unsigned long', even though > the walking of the read value is capped at the specified size. I.e. KVM > is reading memory beyond ctxt->regs_dirty. Functionally it's not an > issue because regs_dirty is in the middle of x86_emulate_ctxt, i.e. KVM > is just reading its own memory, but relying on that coincidence is gross > and unsafe.
Your nearly perfect description misses one important part: in 'struct x86_emulate_ctxt', 'regs_dirty' is actually 'u32' thus all this buzz :-)
> > Signed-off-by: Sean Christopherson <seanjc@google.com> > --- > arch/x86/kvm/emulate.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c > index 89b11e7dca8a..7226a127ccb4 100644 > --- a/arch/x86/kvm/emulate.c > +++ b/arch/x86/kvm/emulate.c > @@ -269,9 +269,10 @@ static ulong *reg_rmw(struct x86_emulate_ctxt *ctxt, unsigned nr) > > static void writeback_registers(struct x86_emulate_ctxt *ctxt) > { > + unsigned long dirty = ctxt->regs_dirty; > unsigned reg; > > - for_each_set_bit(reg, (ulong *)&ctxt->regs_dirty, 16) > + for_each_set_bit(reg, &dirty, 16) > ctxt->ops->write_gpr(ctxt, reg, ctxt->_regs[reg]); > }
Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
-- Vitaly
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