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Re: [Xen-devel] [PATCH v7 01/19] common/symbols: Export hypervisor symbols to privileged guest



On 06/06/2014 01:57 PM, Andrew Cooper wrote:
On 06/06/14 18:39, Boris Ostrovsky wrote:
Export Xen's symbols as {<address><type><name>} triplet via new XENPF_get_symbol
hypercall

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Reviewed-by: Dietmar Hahn <dietmar.hahn@xxxxxxxxxxxxxx>
Tested-by: Dietmar Hahn <dietmar.hahn@xxxxxxxxxxxxxx>
---
  xen/arch/x86/platform_hypercall.c | 21 +++++++++++++++
  xen/common/symbols.c              | 54 +++++++++++++++++++++++++++++++++++++++
  xen/include/public/platform.h     | 19 ++++++++++++++
  xen/include/xen/symbols.h         |  3 +++
  xen/include/xlat.lst              |  1 +
  5 files changed, 98 insertions(+)

diff --git a/xen/arch/x86/platform_hypercall.c 
b/xen/arch/x86/platform_hypercall.c
index 2162811..2c602e7 100644
--- a/xen/arch/x86/platform_hypercall.c
+++ b/xen/arch/x86/platform_hypercall.c
@@ -23,6 +23,7 @@
  #include <xen/cpu.h>
  #include <xen/pmstat.h>
  #include <xen/irq.h>
+#include <xen/symbols.h>
  #include <asm/current.h>
  #include <public/platform.h>
  #include <acpi/cpufreq/processor_perf.h>
@@ -601,6 +602,26 @@ ret_t 
do_platform_op(XEN_GUEST_HANDLE_PARAM(xen_platform_op_t) u_xenpf_op)
      }
      break;
+ case XENPF_get_symbol:
+    {
+        static char name[KSYM_NAME_LEN + 1];
There needs to be some concurrency protection surrounding the use of
this static.  The symbol mutext in xensyms_read() is not sufficient.

As it currently stands, two vcpus issuing this hypercall at the time
will collide and both will get junk back.


We should be protected by xenpf_lock here.



diff --git a/xen/include/public/platform.h b/xen/include/public/platform.h
index 053b9fa..afe301c 100644
--- a/xen/include/public/platform.h
+++ b/xen/include/public/platform.h
@@ -527,6 +527,24 @@ struct xenpf_core_parking {
  typedef struct xenpf_core_parking xenpf_core_parking_t;
  DEFINE_XEN_GUEST_HANDLE(xenpf_core_parking_t);
+#define XENPF_get_symbol 61
+struct xenpf_symdata {
+    /* IN variables */
+    uint32_t namelen; /* size of 'name' buffer */
+
+    /* IN/OUT variables */
+    uint32_t symnum;  /* IN:  Symbol to read                            */
+                      /* OUT: Next available symbol. If same as IN then */
+                      /*      we reached the end                        */
+
+    /* OUT variables */
+    char type;
+    uint64_t address;
+    XEN_GUEST_HANDLE(char) name;
Please can we avoid introducing non-explicitly-width'd types into the
public ABI.

If you swap name and type, use XEN_GUEST_HANDLE_64() and promote type to
a uint32, it should be 32/64 bit safe and not need translating.

I thought we are going via compat_platform_op for 32-bit guests and thus pass pack(4)'d structures so translating is not needed. Is that not true?

(I did test this on 32-bit dom0 and it worked fine, although that alone is probably not a good argument).

-boris

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