From: Julien Grall <jgrall@amazon.com>
Date: Tue, 16 Aug 2022 18:59:54 +0000 (+0100)
Subject: xen/arm: Support properly __ro_after_init on Arm
X-Git-Url: http://xenbits.xensource.com/gitweb?a=commitdiff_plain;h=ace403022358b736755e3042e949540e775c65f1;p=people%2Froyger%2Fxen.git

xen/arm: Support properly __ro_after_init on Arm

__ro_after_init was introduced recently to prevent modifying
some variables after init.

At the moment, on Arm, the variables will still be accessible
because the region permission is not updated.

Address that by moving the sections .data.ro_after_init
out of .data and then map the region read-only once we finish
to boot.

Signed-off-by: Julien Grall <jgrall@amazon.com>
Reviewed-by: Penny Zheng <penny.zheng@arm.com>
Reviewed-by: Bertrand Marquis <bertrand.marquis@arm.com>
Tested-by: Henry Wang <Henry.Wang@arm.com>
---

diff --git a/xen/arch/arm/include/asm/setup.h b/xen/arch/arm/include/asm/setup.h
index 2bb01ecfa8..5815ccf8c5 100644
--- a/xen/arch/arm/include/asm/setup.h
+++ b/xen/arch/arm/include/asm/setup.h
@@ -137,6 +137,8 @@ u32 device_tree_get_u32(const void *fdt, int node,
 int map_range_to_domain(const struct dt_device_node *dev,
                         u64 addr, u64 len, void *data);
 
+extern const char __ro_after_init_start[], __ro_after_init_end[];
+
 #endif
 /*
  * Local variables:
diff --git a/xen/arch/arm/setup.c b/xen/arch/arm/setup.c
index 500307edc0..6e0398f3f6 100644
--- a/xen/arch/arm/setup.c
+++ b/xen/arch/arm/setup.c
@@ -75,10 +75,24 @@ domid_t __read_mostly max_init_domid;
 
 static __used void init_done(void)
 {
+    int rc;
+
     /* Must be done past setting system_state. */
     unregister_init_virtual_region();
 
     free_init_memory();
+
+    /*
+     * We have finished booting. Mark the section .data.ro_after_init
+     * read-only.
+     */
+    rc = modify_xen_mappings((unsigned long)&__ro_after_init_start,
+                             (unsigned long)&__ro_after_init_end,
+                             PAGE_HYPERVISOR_RO);
+    if ( rc )
+        panic("Unable to mark the .data.ro_after_init section read-only (rc = %d)\n",
+              rc);
+
     startup_cpu_idle_loop();
 }
 
diff --git a/xen/arch/arm/xen.lds.S b/xen/arch/arm/xen.lds.S
index 1e986e211f..92c2984052 100644
--- a/xen/arch/arm/xen.lds.S
+++ b/xen/arch/arm/xen.lds.S
@@ -83,6 +83,13 @@ SECTIONS
   _erodata = .;                /* End of read-only data */
 
   . = ALIGN(PAGE_SIZE);
+  .data.ro_after_init : {
+      __ro_after_init_start = .;
+      *(.data.ro_after_init)
+      . = ALIGN(PAGE_SIZE);
+      __ro_after_init_end = .;
+  } : text
+
   .data.read_mostly : {
        /* Exception table */
        __start___ex_table = .;