unimore/kernel-hacking-2024-linux-steffo
unimore/kernel-hacking-2024-linux-steffo
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x86/tdx: Fix "in-kernel MMIO" check

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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: 31d58c4e55 ("x86/tdx: Handle in-kernel MMIO")
Signed-off-by: Alexey Gladkov (Intel) <legion@kernel.org>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
Cc:stable@vger.kernel.org
Link: https://lore.kernel.org/all/565a804b80387970460a4ebc67c88d1380f61ad1.1726237595.git.legion%40kernel.org
This commit is contained in:
Alexey Gladkov (Intel) 2024-09-13 19:05:56 +02:00 committed by Dave Hansen
parent 98f7e32f20
commit d4fc4d0147
1 changed files with 6 additions and 0 deletions
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6
arch/x86/coco/tdx/tdx.c
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@ -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.
*