Commit 8be074a1 authored by Steve Rutherford's avatar Steve Rutherford Committed by Ben Hutchings

KVM: x86: Introduce segmented_write_std

commit 129a72a0 upstream.

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 283c95d0 ("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: default avatarDmitry Vyukov <dvyukov@google.com>
Fixes: 96051572
Fixes: 283c95d0Suggested-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: default avatarSteve Rutherford <srutherford@google.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
[bwh: Backported to 3.16: drop changes to em_fxsave(), em_fxrstor()]
Signed-off-by: default avatarBen Hutchings <ben@decadent.org.uk>
parent 448ec74e
......@@ -744,6 +744,20 @@ 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);
}
/*
* Fetch the next byte of the instruction being emulated which is pointed to
* by ctxt->_eip, then increment ctxt->_eip.
......@@ -3268,7 +3282,7 @@ 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,
return segmented_write_std(ctxt, ctxt->dst.addr.mem,
&desc_ptr, 2 + ctxt->op_bytes);
}
......
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