Re: [PATCH 1/1] tools/libs/light: fix BAR memory address truncation

[Jürgen Groß]

On 10.10.25 10:19, Jan Beulich wrote:

On 10.10.2025 10:00, Jiqian Chen wrote:

64-bit BAR memory address is truncated when removing a passthrough pci
device from guest since it uses "unsigned int".

You talking of address truncation only here, ...

--- a/tools/libs/light/libxl_pci.c
+++ b/tools/libs/light/libxl_pci.c
@@ -2001,7 +2001,8 @@ static void pci_remove_detached(libxl__egc *egc,
  {
      STATE_AO_GC(prs->aodev->ao);
      libxl_ctx *ctx = libxl__gc_owner(gc);
-    unsigned int start = 0, end = 0, flags = 0, size = 0, irq = 0;
+    unsigned long long start = 0, end = 0, flags = 0, size = 0;
+    unsigned int irq = 0;

... does "flags" really need widening, too?

At least on the system I looked the value was printed as a 64-bit one:

# cat /sys/bus/pci/devices/0000:00:00.0/resource
0x0000000000000000 0x0000000000000000 0x0000000000000000
...

So not widening flags would rely on UB to preserve the evaluated PCI_BAR_IO
flag in case the high 32 bits don't contain 0.

@@ -2031,7 +2032,7 @@ static void pci_remove_detached(libxl__egc *egc,
      }

-        if (fscanf(f, "0x%x 0x%x 0x%x\n", &start, &end, &flags) != 3)
+        if (fscanf(f, "0x%llx 0x%llx 0x%llx\n", &start, &end, &flags) != 3)

for (i = 0; i < PROC_PCI_NUM_RESOURCES; i++) {

While touching this, don't we want to drop the stray 0x in here? Their
presence causes bogus input like 0x0x0 to be accepted, afaict.

Hmm, do we really expect a sysfs file to produce bogus output?

Wouldn't it be better to keep the "0x" in order to detect a differing
output format, which could result in silent misbehavior?

I'm not really feeling strong here, as both cases seem highly unlikely.

@@ -2040,7 +2041,7 @@ static void pci_remove_detached(libxl__egc *egc,
                                                   size, 0);
                  if (rc < 0)
                      LOGED(ERROR, domid,
-                          "xc_domain_ioport_permission error 0x%x/0x%x",
+                          "xc_domain_ioport_permission error 0x%llx/0x%llx",
                            start,
                            size);
              } else {
@@ -2050,7 +2051,7 @@ static void pci_remove_detached(libxl__egc *egc,
                                                  0);
                  if (rc < 0)
                      LOGED(ERROR, domid,
-                          "xc_domain_iomem_permission error 0x%x/0x%x",
+                          "xc_domain_iomem_permission error 0x%llx/0x%llx",

In the hypervisor I would request use of %#llx here; not sure what the
toolstack's take on this is.

I'd go a little bit further and request to use uint64_t instead of
"unsigned long long" and then use "#"PRIx64 for the format.


Juergen

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