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KVM: x86: Introduce segmented_write_std

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Introduces segemented_write_std.

Switches from emulated reads/writes to standard read/writes in fxsave,
fxrstor, sgdt, and sidt.  This fixes CVE-2017-2584, a longstanding
kernel memory leak.

Since commit 283c95d0e3 ("KVM: x86: emulate FXSAVE and FXRSTOR",
2016-11-09), which is luckily not yet in any final release, this would
also be an exploitable kernel memory *write*!

Reported-by: Dmitry Vyukov <dvyukov@google.com>
Cc: stable@vger.kernel.org
Fixes: 96051572c8
Fixes: 283c95d0e3
Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Steve Rutherford <srutherford@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Steve Rutherford 2017-01-11 18:28:29 -08:00 committed by Paolo Bonzini
parent cef84c302f
commit 129a72a0d3
1 changed files with 18 additions and 4 deletions
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22
arch/x86/kvm/emulate.c
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@ -818,6 +818,20 @@ static int segmented_read_std(struct x86_emulate_ctxt *ctxt,
return ctxt->ops->read_std(ctxt, linear, data, size, &ctxt->exception);
}
static int segmented_write_std(struct x86_emulate_ctxt *ctxt,
struct segmented_address addr,
void *data,
unsigned int size)
{
int rc;
ulong linear;
rc = linearize(ctxt, addr, size, true, &linear);
if (rc != X86EMUL_CONTINUE)
return rc;
return ctxt->ops->write_std(ctxt, linear, data, size, &ctxt->exception);
}
/*
* Prefetch the remaining bytes of the instruction without crossing page
* boundary if they are not in fetch_cache yet.
@ -3685,8 +3699,8 @@ static int emulate_store_desc_ptr(struct x86_emulate_ctxt *ctxt,
}
/* Disable writeback. */
ctxt->dst.type = OP_NONE;
return segmented_write(ctxt, ctxt->dst.addr.mem,
&desc_ptr, 2 + ctxt->op_bytes);
return segmented_write_std(ctxt, ctxt->dst.addr.mem,
&desc_ptr, 2 + ctxt->op_bytes);
}
static int em_sgdt(struct x86_emulate_ctxt *ctxt)
@ -3932,7 +3946,7 @@ static int em_fxsave(struct x86_emulate_ctxt *ctxt)
else
size = offsetof(struct fxregs_state, xmm_space[0]);
return segmented_write(ctxt, ctxt->memop.addr.mem, &fx_state, size);
return segmented_write_std(ctxt, ctxt->memop.addr.mem, &fx_state, size);
}
static int fxrstor_fixup(struct x86_emulate_ctxt *ctxt,
@ -3974,7 +3988,7 @@ static int em_fxrstor(struct x86_emulate_ctxt *ctxt)
if (rc != X86EMUL_CONTINUE)
return rc;
rc = segmented_read(ctxt, ctxt->memop.addr.mem, &fx_state, 512);
rc = segmented_read_std(ctxt, ctxt->memop.addr.mem, &fx_state, 512);
if (rc != X86EMUL_CONTINUE)
return rc;