x86/kaslr: Add a check that the random address is in range

Check in find_random_phys_addr() that the chosen address is inside the
range that was required.

Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20200728225722.67457-22-nivedita@alum.mit.edu

diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
index 80cdd20..735fcb2 100644 (file)
--- a/arch/x86/boot/compressed/kaslr.c
+++ b/arch/x86/boot/compressed/kaslr.c
@@ -803,6 +803,8 @@ static void process_e820_entries(unsigned long minimum,
 static unsigned long find_random_phys_addr(unsigned long minimum,
                                           unsigned long image_size)
 {
+       u64 phys_addr;
+
        /* Bail out early if it's impossible to succeed. */
        if (minimum + image_size > mem_limit)
                return 0;
@@ -816,7 +818,15 @@ static unsigned long find_random_phys_addr(unsigned long minimum,
        if (!process_efi_entries(minimum, image_size))
                process_e820_entries(minimum, image_size);
 
-       return slots_fetch_random();
+       phys_addr = slots_fetch_random();
+
+       /* Perform a final check to make sure the address is in range. */
+       if (phys_addr < minimum || phys_addr + image_size > mem_limit) {
+               warn("Invalid physical address chosen!\n");
+               return 0;
+       }
+
+       return (unsigned long)phys_addr;
 }
 
 static unsigned long find_random_virt_addr(unsigned long minimum,