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Re: [Xen-devel] [PATCH v5 6/7] xen/arm: don't iomem_permit_access for reserved-memory regions


On 8/13/19 3:34 PM, Volodymyr Babchuk wrote:

Stefano Stabellini writes:

Don't allow reserved-memory regions to be remapped into any unprivileged
guests, until reserved-memory regions are properly supported in Xen. For
now, do not call iomem_permit_access on them, because giving
iomem_permit_access to dom0 means that the toolstack will be able to
assign the region to a domU.

Signed-off-by: Stefano Stabellini <stefanos@xxxxxxxxxx>

Changes in v5:
- fix check condition
- use strnicmp
- return error
- improve commit message

Changes in v4:
- compare the parent name with reserved-memory
- use dt_node_cmp

Changes in v3:
- new patch
  xen/arch/arm/domain_build.c | 24 ++++++++++++++++--------
  1 file changed, 16 insertions(+), 8 deletions(-)

diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
index 4c8404155a..e0c0c01c88 100644
--- a/xen/arch/arm/domain_build.c
+++ b/xen/arch/arm/domain_build.c
@@ -1155,15 +1155,23 @@ static int __init map_range_to_domain(const struct 
dt_device_node *dev,
      bool need_mapping = !dt_device_for_passthrough(dev);
      int res;
- res = iomem_permit_access(d, paddr_to_pfn(addr),
-                              paddr_to_pfn(PAGE_ALIGN(addr + len - 1)));
-    if ( res )
+    /*
+     * Don't give iomem permissions for reserved-memory ranges to domUs
+     * until reserved-memory support is complete.
+     */
+    if ( strnicmp(dt_node_full_name(dev), "/reserved-memory",
+         strlen("/reserved-memory")) != 0 )
Why are you using strnicmp there? With such usage it is the same as

Definitely not, strcasecmp() will compare that the two strings exactly match (ignoring the case of the characters). Here we only want to check the first part of the patch, so we need to use the length-limited version.

But, if you want to find "/reserved-memory" anywhere in
dt_node_full_name(dev), then you probably want to use strcasestr()

For a first strcasestr() is not provided by the string lib in Xen. So you would need to implement it.

But then all the reserved-memory regions are under the node /reserved-memory. A path /a/b/reserved-memory is not a valid memory region.

On a side note, the check is still incorrect here because you would allow /reserved-memory@... or /reserved-memory-test to pass.


Julien Grall

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