Prevent access to per-core variables without proper macro

Without this patch, it's possible to declare a per-core variable
like so:

    declare_per_core! {
        static mut TIMER_WHEEL: Option<TimerWheel> = None;
    }

Then access the variable like:

    unsafe {
        TIMER_WHEEL = Some(value);
    }

But this will always mutate the value on the BSP core (and is not
thread-safe). This patch generates a new symbol for the actual
static variable, which effectively requires the usage of the
'get_per_core' or 'get_per_core_mut' and prevents this category
of error.

Author: ALSchwalm

mythril/Cargo.lock

@@ -20,6 +20,7 @@ linked_list_allocator = "0.8.6"
 log = { version = "0.4.8", default-features = false }
 multiboot = "0.3.0"
 multiboot2 = "0.9.0"
+paste = "1.0"
 raw-cpuid = "8.1.1"
 rlibc = "1.0.0"
 serde = {version = "^1", default-features = false, features = ["alloc", "derive"] }

mythril/Cargo.toml

@@ -127,7 +127,9 @@ macro_rules! get_per_core {
     ($name:ident) => {
         #[allow(unused_unsafe)]
         unsafe {
-            $crate::percore::get_per_core_impl(&$name)
+            $crate::percore::get_per_core_impl(&paste::paste! {
+                [<PERCORE_ $name>]
+            })
         }
     };
 }
@@ -137,7 +139,9 @@ macro_rules! get_per_core_mut {
     ($name:ident) => {
         #[allow(unused_unsafe)]
         unsafe {
-            $crate::percore::get_per_core_mut_impl(&mut $name)
+            $crate::percore::get_per_core_mut_impl(&mut paste::paste! {
+                [<PERCORE_ $name>]
+            })
         }
     };
 }
@@ -147,14 +151,19 @@ macro_rules! get_per_core_mut {
 #[doc(hidden)]
 macro_rules! __declare_per_core_internal {
     ($(#[$attr:meta])* ($($vis:tt)*) static mut $N:ident : $T:ty = $e:expr; $($t:tt)*) => {
-        #[link_section = ".per_core"]
-        $($vis)* static mut $N: $T = $e;
+        paste::paste! {
+            #[link_section = ".per_core"]
+            $($vis)* static mut [<PERCORE_ $N>]: $T = $e;
+        }
 
         declare_per_core!($($t)*);
     };
     ($(#[$attr:meta])* ($($vis:tt)*) static $N:ident : $T:ty = $e:expr; $($t:tt)*) => {
-        #[link_section = ".per_core"]
-        $($vis)* static $N: $T = $e;
+        use paste::paste;
+        paste! {
+            #[link_section = ".per_core"]
+            $($vis)* static [<PERCORE_ $N>]: $T = $e;
+        }
 
         declare_per_core!($($t)*);
     };