[tip: x86/urgent] x86/tdx: Fix data leak in mmio_read()

["tip-bot2 for Kirill A. Shutemov" <tip-bot2@linutronix.de>]

The following commit has been merged into the x86/urgent branch of tip:

Commit-ID:     b6fb565a2d15277896583d471b21bc14a0c99661
Gitweb:        https://git.kernel.org/tip/b6fb565a2d15277896583d471b21bc14a0c99661
Author:        Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
AuthorDate:    Mon, 26 Aug 2024 15:53:04 +03:00
Committer:     Dave Hansen <dave.hansen@linux.intel.com>
CommitterDate: Mon, 26 Aug 2024 12:45:19 -07:00

x86/tdx: Fix data leak in mmio_read()

The mmio_read() function makes a TDVMCALL to retrieve MMIO data for an
address from the VMM.

Sean noticed that mmio_read() unintentionally exposes the value of an
initialized variable (val) on the stack to the VMM.

This variable is only needed as an output value. It did not need to be
passed to the VMM in the first place.

Do not send the original value of *val to the VMM.

[ dhansen: clarify what 'val' is used for. ]

Fixes: 31d58c4e557d ("x86/tdx: Handle in-kernel MMIO")
Reported-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Cc:stable@vger.kernel.org
Link: https://lore.kernel.org/all/20240826125304.1566719-1-kirill.shutemov%40linux.intel.com
---
 arch/x86/coco/tdx/tdx.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c
index 078e2ba..da8b66d 100644
--- a/arch/x86/coco/tdx/tdx.c
+++ b/arch/x86/coco/tdx/tdx.c
@@ -389,7 +389,6 @@ static bool mmio_read(int size, unsigned long addr, unsigned long *val)
 		.r12 = size,
 		.r13 = EPT_READ,
 		.r14 = addr,
-		.r15 = *val,
 	};
 
 	if (__tdx_hypercall(&args))