[Xen-changelog] [xen stable-4.9] common/gnttab: Introduce command line feature controls

[patchbot@xxxxxxx]

commit 023da62e97afe33347feeaac5be3769fcb45c313
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Tue Aug 14 11:20:53 2018 +0100
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Tue Aug 14 12:33:45 2018 +0100

    common/gnttab: Introduce command line feature controls
    
    This patch was originally released as part of XSA-226.  It retains the same
    command line syntax (as various downstreams are mitigating XSA-226 using 
this
    mechanism) but the defaults have been updated due to the revised XSA-226
    patched, after which transitive grants are believed to functioning
    properly.
    
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    (cherry picked from commit dc96c65ed6d7ffd4c95487373df708d97443cf77)
---
 docs/misc/xen-command-line.markdown | 13 ++++++++++++
 xen/common/grant_table.c            | 42 ++++++++++++++++++++++++++++++++++++-
 2 files changed, 54 insertions(+), 1 deletion(-)

diff --git a/docs/misc/xen-command-line.markdown 
b/docs/misc/xen-command-line.markdown
index fa1f11e27f..0f0376da81 100644
--- a/docs/misc/xen-command-line.markdown
+++ b/docs/misc/xen-command-line.markdown
@@ -872,6 +872,19 @@ Controls EPT related features.
 
 Specify which console gdbstub should use. See **console**.
 
+### gnttab
+> `= List of [ max-ver:<integer>, transitive=<bool> ]`
+
+> Default: `gnttab=max-ver:2,transitive`
+
+Control various aspects of the grant table behaviour available to guests.
+
+* `max-ver` Select the maximum grant table version to offer to guests.  Valid
+version are 1 and 2.
+* `transitive` Permit or disallow the use of transitive grants.  Note that the
+use of grant table v2 without transitive grants is an ABI breakage from the
+guests point of view.
+
 ### gnttab\_max\_frames
 > `= <integer>`
 
diff --git a/xen/common/grant_table.c b/xen/common/grant_table.c
index 5badc58677..95f9443ce8 100644
--- a/xen/common/grant_table.c
+++ b/xen/common/grant_table.c
@@ -62,6 +62,41 @@ integer_param("gnttab_max_frames", max_grant_frames);
 static unsigned int __read_mostly max_maptrack_frames;
 integer_param("gnttab_max_maptrack_frames", max_maptrack_frames);
 
+static unsigned int __read_mostly opt_gnttab_max_version = 2;
+static bool __read_mostly opt_transitive_grants = true;
+
+static int __init parse_gnttab(const char *s)
+{
+    const char *ss, *e;
+    int val, rc = 0;
+
+    do {
+        ss = strchr(s, ',');
+        if ( !ss )
+            ss = strchr(s, '\0');
+
+        if ( !strncmp(s, "max-ver:", 8) ||
+             !strncmp(s, "max_ver:", 8) ) /* Alias for original XSA-226 patch 
*/
+        {
+            long ver = simple_strtol(s + 8, &e, 10);
+
+            if ( e == ss && ver >= 1 && ver <= 2 )
+                opt_gnttab_max_version = ver;
+            else
+                rc = -EINVAL;
+        }
+        else if ( (val = parse_boolean("transitive", s, ss)) >= 0 )
+            opt_transitive_grants = val;
+        else
+            rc = -EINVAL;
+
+        s = ss + 1;
+    } while ( *ss );
+
+    return rc;
+}
+custom_param("gnttab", parse_gnttab);
+
 /*
  * Note that the three values below are effectively part of the ABI, even if
  * we don't need to make them a formal part of it: A guest suspended for
@@ -2538,7 +2573,8 @@ static int gnttab_copy_claim_buf(const struct gnttab_copy 
*op,
                                       current->domain->domain_id,
                                       buf->read_only,
                                       &buf->frame, &buf->page,
-                                      &buf->ptr.offset, &buf->len, 1);
+                                      &buf->ptr.offset, &buf->len,
+                                      opt_transitive_grants);
         if ( rc != GNTST_okay )
             goto out;
         buf->ptr.u.ref = ptr->u.ref;
@@ -2739,6 +2775,10 @@ 
gnttab_set_version(XEN_GUEST_HANDLE_PARAM(gnttab_set_version_t) uop)
     if ( op.version != 1 && op.version != 2 )
         goto out;
 
+    res = -ENOSYS;
+    if ( op.version == 2 && opt_gnttab_max_version == 1 )
+        goto out; /* Behave as before set_version was introduced. */
+
     res = 0;
     if ( gt->gt_version == op.version )
         goto out;
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.9

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