drm/imagination: Fixed infinite loop in pvr_vm_mips_map()

Unwinding loop in error path for this function uses unsigned limit
variable, causing the promotion of the signed counter variable.

--> 204         for (; pfn >= start_pfn; pfn--)
                       ^^^^^^^^^^^^^^^^
If start_pfn can be zero then this is an endless loop.  I've seen this
code in other places as well.  This loop is slightly off as well.  It
should decrement pfn on the first iteration.

Fix by making the loop limit variables signed. Also fix missing
predecrement by modifying to while loop.

Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Signed-off-by: Donald Robson <donald.robson@imgtec.com>
Signed-off-by: Maxime Ripard <mripard@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20231208160825.92933-1-donald.robson@imgtec.com

diff --git a/drivers/gpu/drm/imagination/pvr_vm_mips.c b/drivers/gpu/drm/imagination/pvr_vm_mips.c
index 2bc7181a4c3ebe6f7825aa29f90c8da9e2cee397..b7fef3c797e6caca1cac6a48476404d0d5b0359a 100644 (file)
--- a/drivers/gpu/drm/imagination/pvr_vm_mips.c
+++ b/drivers/gpu/drm/imagination/pvr_vm_mips.c
@@ -152,8 +152,8 @@ pvr_vm_mips_map(struct pvr_device *pvr_dev, struct pvr_fw_object *fw_obj)
        u64 end;
        u32 cache_policy;
        u32 pte_flags;
-       u32 start_pfn;
-       u32 end_pfn;
+       s32 start_pfn;
+       s32 end_pfn;
        s32 pfn;
        int err;
 
@@ -201,7 +201,7 @@ pvr_vm_mips_map(struct pvr_device *pvr_dev, struct pvr_fw_object *fw_obj)
        return 0;
 
 err_unmap_pages:
-       for (; pfn >= start_pfn; pfn--)
+       while (--pfn >= start_pfn)
                WRITE_ONCE(mips_data->pt[pfn], 0);
 
        pvr_mmu_flush_request_all(pvr_dev);