[PATCH v2 14/14] x86/PVH: check Dom0 start_info for truncation; adjust entrypoint type

[Jan Beulich <jbeulich@xxxxxxxx>]

While for start_info we now (supposedly) guarantee that it lives below
4Gb, check it nevertheless to play/stay safe.

For the entrypoint address the situation is different: libelf already
hands us a 32-bit quantity; if there was truncation there, it would be
inside libelf (when extracting the value from the ELF notes). Reflect
the 32-bit-ness in types used.

Requested-by: Roger Pau Monné <roger@xxxxxxxxxxxxxx>
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
v2: New.

--- a/xen/arch/x86/hvm/dom0_build.c
+++ b/xen/arch/x86/hvm/dom0_build.c
@@ -798,7 +798,7 @@ static bool __init check_and_adjust_load
 static int __init pvh_place_kernel(
     const struct boot_domain *bd,
     struct elf_binary *elf,
-    paddr_t *entry)
+    uint32_t *entry)
 {
     struct domain *d = bd->d;
     struct boot_module *image = bd->kernel;
@@ -1097,7 +1097,7 @@ static int __init pvh_load_kernel(
     return 0;
 }
 
-static int __init pvh_setup_cpus(struct domain *d, paddr_t entry,
+static int __init pvh_setup_cpus(struct domain *d, uint32_t entry,
                                  paddr_t start_info)
 {
     struct vcpu *v = d->vcpu[0];
@@ -1123,6 +1123,13 @@ static int __init pvh_setup_cpus(struct
         .cpu_regs.x86_32.tr_ar = 0x8b,
     };
 
+    if ( cpu_ctx.cpu_regs.x86_32.ebx != start_info )
+    {
+        printk("%pd: start-info address truncation: %p)\n",
+               d, _p(start_info));
+        return -ERANGE;
+    }
+
     sched_setup_dom0_vcpus(d);
 
     rc = arch_set_info_hvm_guest(v, &cpu_ctx);
@@ -1640,7 +1647,7 @@ static void __init pvh_setup_mmcfg(struc
 
 int __init dom0_construct_pvh(const struct boot_domain *bd)
 {
-    paddr_t entry, start_info;
+    uint32_t entry;
     struct domain *d = bd->d;
     struct elf_binary elf;
     struct e820entry *orig_e820;
@@ -1649,7 +1656,7 @@ int __init dom0_construct_pvh(const stru
     struct acpi_info acpi = {};
     struct vmx_info vmx = {};
     struct hvm_modlist_entry initrd = {};
-    paddr_t blob_start, blob_end;
+    paddr_t start_info, blob_start, blob_end;
     int rc;
 
     printk(XENLOG_INFO "*** Building a PVH Dom%d ***\n", d->domain_id);