[xen stable-4.9] xen/domctl: Fix Xen heap leak via XEN_DOMCTL_getvcpucontext

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[xen stable-4.9] xen/domctl: Fix Xen heap leak via XEN_DOMCTL_getvcpucontext

patchbot
commit de76106618e36a1be8ffc6bf5f0103a65039f6a4
Author:     Andrew Cooper <[hidden email]>
AuthorDate: Tue Oct 24 16:11:24 2017 +0200
Commit:     Jan Beulich <[hidden email]>
CommitDate: Tue Oct 24 16:11:24 2017 +0200

    xen/domctl: Fix Xen heap leak via XEN_DOMCTL_getvcpucontext
   
    The backing structure for XEN_DOMCTL_getvcpucontext is only zeroed in the x86
    HVM case.  At the very least, this means that ARM returns junk through its
    flags field (as it is only ever conditionally or'd into), and x86 PV leaks
    data through gdt_frames[14...15].  (An exhaustive search for other leaks
    hasn't been performed).
   
    Unconditionally zero the memory upon allocation, and forgo the double clear
    for x86 HVM.  These hypercalls are not on hotpaths.
   
    Note that this does not qualify for an XSA.  Per XSA-77,
    XEN_DOMCTL_getvcpucontext is unsafe for disaggregation, meaning that only the
    control domain can use this hypercall.
   
    Signed-off-by: Andrew Cooper <[hidden email]>
    Reviewed-by: Jan Beulich <[hidden email]>
    master commit: 3b2eeb7412e529f38d1e8b872ba0bc6ab09a7008
    master date: 2017-10-09 12:43:21 +0100
---
 xen/arch/x86/domctl.c | 2 --
 xen/common/domctl.c   | 2 +-
 2 files changed, 1 insertion(+), 3 deletions(-)

diff --git a/xen/arch/x86/domctl.c b/xen/arch/x86/domctl.c
index e104be2..d32c4fa 100644
--- a/xen/arch/x86/domctl.c
+++ b/xen/arch/x86/domctl.c
@@ -1489,8 +1489,6 @@ void arch_get_info_guest(struct vcpu *v, vcpu_guest_context_u c)
     bool_t compat = is_pv_32bit_domain(d);
 #define c(fld) (!compat ? (c.nat->fld) : (c.cmp->fld))
 
-    if ( !is_pv_domain(d) )
-        memset(c.nat, 0, sizeof(*c.nat));
     memcpy(&c.nat->fpu_ctxt, v->arch.fpu_ctxt, sizeof(c.nat->fpu_ctxt));
     c(flags = v->arch.vgc_flags & ~(VGCF_i387_valid|VGCF_in_kernel));
     if ( v->fpu_initialised )
diff --git a/xen/common/domctl.c b/xen/common/domctl.c
index 951a5dc..011a7de 100644
--- a/xen/common/domctl.c
+++ b/xen/common/domctl.c
@@ -864,7 +864,7 @@ long do_domctl(XEN_GUEST_HANDLE_PARAM(xen_domctl_t) u_domctl)
                      < sizeof(struct compat_vcpu_guest_context));
 #endif
         ret = -ENOMEM;
-        if ( (c.nat = xmalloc(struct vcpu_guest_context)) == NULL )
+        if ( (c.nat = xzalloc(struct vcpu_guest_context)) == NULL )
             goto getvcpucontext_out;
 
         vcpu_pause(v);
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.9

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