Commit d4fc4d01 authored by Alexey Gladkov (Intel)'s avatar Alexey Gladkov (Intel) Committed by Dave Hansen
Browse files

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: 31d58c4e ("x86/tdx: Handle in-kernel MMIO")
Signed-off-by: default avatarAlexey Gladkov (Intel) <legion@kernel.org>
Signed-off-by: default avatarDave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: default avatarKirill A. Shutemov <kirill.shutemov@linux.intel.com>
Acked-by: default avatarDave Hansen <dave.hansen@linux.intel.com>
Cc:stable@vger.kernel.org
Link: https://lore.kernel.org/all/565a804b80387970460a4ebc67c88d1380f61ad1.1726237595.git.legion%40kernel.org
parent 98f7e32f

arch/x86/coco/tdx/tdx.c

+6 −0
Original line number Diff line number Diff line
@@ -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.

	 *