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

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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: Vitaly Kuznetsov <vkuznets@redhat.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20220526210817.3428868-2-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson
2022-05-26 21:08:10 +00:00
committed by Paolo Bonzini
parent e15f5e6fa6
commit 61d9c412d0
1 changed files with 2 additions and 1 deletions
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3
arch/x86/kvm/emulate.c
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@@ -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]);
}