Correctly check return code from vram2PRAMIN()

Blindly using an invalid return address was resulting in undefined
behavior due to traversal of non-page-table addresses as though they
were part of the page table.

1 files changed, 12 insertions, 5 deletions

diff --git a/mmu.c b/mmu.c
index 30e9362..e420864 100644
--- a/mmu.c
+++ b/mmu.c
@@ -15,11 +15,12 @@
 
 /* Convert a physical VRAM address to an offset in the PRAMIN window
   @param addr VRAM address to convert
-  @return 0 on error, PRAMIN offset on success
+  @return -errno on error, PRAMIN offset on success
 
   Note: Use off2PRAMIN() instead if you want a dereferenceable address
+  Note: PRAMIN window is only 1MB, so returning an int is safe
 */
-uint32_t vram2PRAMIN(struct nvdebug_state *g, uint64_t addr) {
+static int vram2PRAMIN(struct nvdebug_state *g, uint64_t addr) {
         uint64_t pramin_base_va;
         bar0_window_t window;
         window.raw = nvdebug_readl(g, NV_PBUS_BAR0_WINDOW);
@@ -27,20 +28,26 @@ uint32_t vram2PRAMIN(struct nvdebug_state *g, uint64_t addr) {
         if (addr & ~0x0001ffffffffffff) {
                 printk(KERN_ERR "[nvdebug] Invalid address %llx passed to %s!\n",
                        addr, __func__);
-                return 0;
+                return -EINVAL;
         }
         // For unclear (debugging?) reasons, PRAMIN can point to SYSMEM
         if (window.target != TARGET_VID_MEM)
-                return 0;
+                return -EFAULT;
         pramin_base_va = ((uint64_t)window.base) << 16;
         // Protect against out-of-bounds accesses
         if (addr < pramin_base_va || addr > pramin_base_va + NV_PRAMIN_LEN)
-                return 0;
+                return -ERANGE;
         return addr - pramin_base_va;
 }
 
 // Convert a GPU physical address to CPU virtual address via the PRAMIN window
+// @return A dereferencable address, or 0 (an invalid physical address) on err
 void __iomem *phy2PRAMIN(struct nvdebug_state* g, uint64_t phy) {
+        int off = vram2PRAMIN(g, phy);
+        if (off == -ERANGE)
+                printk(KERN_ERR "[nvdebug] Page table walk off end of PRAMIN!\n");
+        if (off < 0)
+                return 0;
         return g->regs + NV_PRAMIN + vram2PRAMIN(g, phy);
 }