Commit 61d9c412 authored by Sean Christopherson's avatar Sean Christopherson Committed by Paolo Bonzini
Browse files

KVM: x86: Grab regs_dirty in local 'unsigned long' 



Capture ctxt->regs_dirty in a local 'unsigned long' instead of casting it
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. 64-bit KVM is reading
memory beyond ctxt->regs_dirty, which is a u32 and thus 4 bytes, whereas
an unsigned long is 8 bytes.  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.

Reviewed-by: default avatarVitaly Kuznetsov <vkuznets@redhat.com>
Reviewed-by: default avatarKees Cook <keescook@chromium.org>
Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
Message-Id: <20220526210817.3428868-2-seanjc@google.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent e15f5e6f

arch/x86/kvm/emulate.c

+2 −1
Original line number Diff line number Diff line
@@ -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]);

}