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

[tip-bot2 for Kirill A. Shutemov]

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

Commit-ID:     eb786ee1390b8fbba633c01a971709c6906fd8bf
Gitweb:        https://git.kernel.org/tip/eb786ee1390b8fbba633c01a971709c6906fd8bf
Author:        Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
AuthorDate:    Mon, 26 Aug 2024 15:53:04 +03:00
Committer:     Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
CommitterDate: Mon, 26 Aug 2024 07:04:09 -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 on the stack to the VMM.

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

Fixes: 31d58c4e557d ("x86/tdx: Handle in-kernel MMIO")
Reported-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc:stable@xxxxxxxxxxxxxxx
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))