CVE-2022-48853Reinstate some of "swiotlb: rework "fix info leak with DMA_FROM_DEVICE""

Official description

In the Linux kernel, the following vulnerability has been resolved: swiotlb: fix info leak with DMA_FROM_DEVICE The problem I'm addressing was discovered by the LTP test covering cve-2018-1000204. A short description of what happens follows: 1) The test case issues a command code 00 (TEST UNIT READY) via the SG_IO interface with: dxfer_len == 524288, dxdfer_dir == SG_DXFER_FROM_DEV and a corresponding dxferp. The peculiar thing about this is that TUR is not reading from the device. 2) In sg_start_req() the invocation of blk_rq_map_user() effectively bounces the user-space buffer. As if the device was to transfer into it. Since commit a45b599ad808 ("scsi: sg: allocate with __GFP_ZERO in sg_build_indirect()") we make sure this first bounce buffer is allocated with GFP_ZERO. 3) For the rest of the story we keep ignoring that we have a TUR, so the device won't touch the buffer we prepare as if the we had a DMA_FROM_DEVICE type of situation. My setup uses a virtio-scsi device and the buffer allocated by SG is mapped by the function virtqueue_add_split() which uses DMA_FROM_DEVICE for the "in" sgs (here scatter-gather and not scsi generics). This mapping involves bouncing via the swiotlb (we need swiotlb to do virtio in protected guest like s390 Secure Execution, or AMD SEV). 4) When the SCSI TUR is done, we first copy back the content of the second (that is swiotlb) bounce buffer (which most likely contains some previous IO data), to the first bounce buffer, which contains all zeros. Then we copy back the content of the first bounce buffer to the user-space buffer. 5) The test case detects that the buffer, which it zero-initialized, ain't all zeros and fails. One can argue that this is an swiotlb problem, because without swiotlb we leak all zeros, and the swiotlb should be transparent in a sense that it does not affect the outcome (if all other participants are well behaved). Copying the content of the original buffer into the swiotlb buffer is the only way I can think of to make swiotlb transparent in such scenarios. So let's do just that if in doubt, but allow the driver to tell us that the whole mapped buffer is going to be overwritten, in which case we can preserve the old behavior and avoid the performance impact of the extra bounce.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/fd97de9c7b973f46a6103f4170c5efc7b8ef8797
• https://git.kernel.org/stable/c/aaf166f37eb6bb55d81c3e40a2a460c8875c8813
• https://git.kernel.org/stable/c/06cb238b0f7ac1669cb06390704c61794724c191
• https://git.kernel.org/stable/c/b2f140a9f980806f572d672e1780acea66b9a25c
• https://git.kernel.org/stable/c/f3f2247ac31cb71d1f05f56536df5946c6652f4a
• https://git.kernel.org/stable/c/7007c894631cf43041dcfa0da7142bbaa7eb673c
• https://git.kernel.org/stable/c/dcead36b19d999d687cd9c99b7f37520d9102b57
• https://git.kernel.org/stable/c/f2141881b530738777c28bb51c62175895c8178b
• https://git.kernel.org/stable/c/901c7280ca0d5e2b4a8929fbe0bfb007ac2a6544
• https://git.kernel.org/stable/c/c132f2ba716b5ee6b35f82226a6e5417d013d753 x_transferred
• https://git.kernel.org/stable/c/971e5dadffd02beba1063e7dd9c3a82de17cf534 x_transferred
• https://git.kernel.org/stable/c/8d9ac1b6665c73f23e963775f85d99679fd8e192 x_transferred
• https://git.kernel.org/stable/c/6bfc5377a210dbda2a237f16d94d1bd4f1335026 x_transferred
• https://git.kernel.org/stable/c/d4d975e7921079f877f828099bb8260af335508f x_transferred
• https://git.kernel.org/stable/c/7403f4118ab94be837ab9d770507537a8057bc63 x_transferred
• https://git.kernel.org/stable/c/270475d6d2410ec66e971bf181afe1958dad565e x_transferred
• https://git.kernel.org/stable/c/ddbd89deb7d32b1fbb879f48d68fda1a8ac58e8e x_transferred