On Fri, 9 Mar 2018, Kees Cook wrote:
> Avoid VLAs[1] by always allocating the upper bound of stack space
> needed. The existing users of rslib appear to max out at 32 roots,
> so use that as the upper bound.
I think 32 is plenty. Do we have actually a user with 32?
> Alternative: make init_rs() a true caller-instance and pre-allocate
> the workspaces. Will this need locking or are the callers already
> single-threaded in their use of librs?
init_rs() is an init function which needs to be invoked _before_ the
decoder/encoder can be used.
The way it works today that it can share the rs_control between users to
avoid duplicating the polynom arrays and the setup of them.
So we might change how rs_control works and allocate rs_control for each
invocation of init_rs(). That means we need two data structures:
Rename rs_control to rs_poly and just use that internaly for sharing the
polynom arrays.
rs_control then becomes:
struct rs_control {
struct rs_poly *poly;
uint16_t lamda[MAX_ROOTS + 1];
....
uint16_t loc[MAX_ROOTS];
};
But as you said that requires serialization or separation at the usage
sites.
drivers/mtd/nand/* would either need a mutex or allocate one rs_control per
instance. Simple enough to do.
drivers/md/dm-verity-fec.c looks like it's allocating a dm control struct
for each worker thread, so that should just require allocating one
rs_control per worker then.
pstore only has an issue in case of OOPS. A simple solution would be to
allocate two rs_control structs, one for regular usage and one for the OOPS
case. Not sure if that covers all possible problems, so that needs more
thoughts.
Thanks,
tglx
