x86/tdx: Fix "in-kernel MMIO" check

TDX only supports kernel-initiated MMIO operations. The handle_mmio()
function checks if the #VE exception occurred in the kernel and rejects
the operation if it did not.

However, userspace can deceive the kernel into performing MMIO on its
behalf. For example, if userspace can point a syscall to an MMIO address,
syscall does get_user() or put_user() on it, triggering MMIO #VE. The
kernel will treat the #VE as in-kernel MMIO.

Ensure that the target MMIO address is within the kernel before decoding
instruction.

Fixes: 31d58c4e557d ("x86/tdx: Handle in-kernel MMIO")
Signed-off-by: Alexey Gladkov (Intel) <[email protected]>
Signed-off-by: Dave Hansen <[email protected]>
Reviewed-by: Kirill A. Shutemov <[email protected]>
Acked-by: Dave Hansen <[email protected]>
Cc:[email protected]
Link: https://lore.kernel.org/all/565a804b80387970460a4ebc67c88d1380f61ad1.1726237595.git.legion%40kernel.org

diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c
index da8b66dce0da5f614f217c3d5d9bbe978e458ceb..327c45c5013fea31fbbb34d8192f3d8f8b0b58fd 100644 (file)
--- a/arch/x86/coco/tdx/tdx.c
+++ b/arch/x86/coco/tdx/tdx.c
@@ -16,6 +16,7 @@
 #include <asm/insn-eval.h>
 #include <asm/pgtable.h>
 #include <asm/set_memory.h>
+#include <asm/traps.h>
 
 /* MMIO direction */
 #define EPT_READ       0
@@ -433,6 +434,11 @@ static int handle_mmio(struct pt_regs *regs, struct ve_info *ve)
                        return -EINVAL;
        }
 
+       if (!fault_in_kernel_space(ve->gla)) {
+               WARN_ONCE(1, "Access to userspace address is not supported");
+               return -EINVAL;
+       }
+
        /*
         * Reject EPT violation #VEs that split pages.
         *