virt: sevguest: Fix passing a stack buffer as a scatterlist target

CONFIG_DEBUG_SG highlights that get_{report,ext_report,derived_key)()}
are passing stack buffers as the @req_buf argument to
handle_guest_request(), generating a Call Trace of the following form:

    WARNING: CPU: 0 PID: 1175 at include/linux/scatterlist.h:187 enc_dec_message+0x518/0x5b0 [sev_guest]
    [..]
    Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/26/2023
    RIP: 0010:enc_dec_message+0x518/0x5b0 [sev_guest]
    Call Trace:
     <TASK>
    [..]
     handle_guest_request+0x135/0x520 [sev_guest]
     get_ext_report+0x1ec/0x3e0 [sev_guest]
     snp_guest_ioctl+0x157/0x200 [sev_guest]

Note that the above Call Trace was with the DEBUG_SG BUG_ON()s converted
to WARN_ON()s.

This is benign as long as there are no hardware crypto accelerators
loaded for the aead cipher, and no subsequent dma_map_sg() is performed
on the scatterlist. However, sev-guest can not assume the presence of
an aead accelerator nor can it assume that CONFIG_DEBUG_SG is disabled.

Resolve this bug by allocating virt_addr_valid() memory, similar to the
other buffers am @snp_dev instance carries, to marshal requests from
user buffers to kernel buffers.

Reported-by: Peter Gonda <[email protected]>
Closes: http://lore.kernel.org/r/CAMkAt6r2VPPMZ__SQfJse8qWsUyYW3AgYbOUVM0S_Vtk=KvkxQ@mail.gmail.com
Fixes: fce96cf04430 ("virt: Add SEV-SNP guest driver")
Cc: Borislav Petkov <[email protected]>
Cc: Tom Lendacky <[email protected]>
Cc: Dionna Glaze <[email protected]>
Cc: Jeremi Piotrowski <[email protected]>
Tested-by: Kuppuswamy Sathyanarayanan <[email protected]>
Reviewed-by: Tom Lendacky <[email protected]>
Signed-off-by: Dan Williams <[email protected]>

0 files changed, 0 insertions, 0 deletions