[EXTERNAL] Re: Proposal for a New Command to U-Boot Fuse Programming

[Tom Rini]

On Fri, Jan 24, 2025 at 02:31:15PM +0530, Harsha Vardhan V M wrote:
> 
> 
> On 22/01/25 22:52, Tom Rini wrote:
> > On Fri, Jan 10, 2025 at 11:12:47AM +0530, Harsha Vardhan V M wrote:
> > > 
> > > 
> > > On 07/01/25 03:53, Tom Rini wrote:
> > > > On Mon, Jan 06, 2025 at 12:06:25PM +0530, Harsha Vardhan V M wrote:
> > > > 
> > > > > I would like to propose a new command for U-Boot's fuse programming
> > > > > functionality to address the challenges posed by the current implementation.
> > > > > While the existing fuse prog command works well for programming individual
> > > > > fuse values, it becomes cumbersome especially when dealing with large-scale
> > > > > programming requirements.
> > > > > 
> > > > > Current Command: fuse prog [-y] <bank> <word> <hexval> [<hexval>...]
> > > > > 
> > > > > This command programs one or more fuse words starting from a specific <bank>
> > > > > and <word> with the hex values given as input.
> > > > > 
> > > > > While functional, it lacks the efficiency and robustness needed for
> > > > > programming a significant number of fuses or handling structured fuse
> > > > > configuration data. Repeatedly specifying values for each fuse bank and word
> > > > > is not only time-consuming but also prone to errors during manual input or
> > > > > scripting. This approach does not leverage the ability to process
> > > > > pre-structured data in memory. For users with complex programming needs, the
> > > > > current method becomes an obstacle rather than a tool.
> > > > > 
> > > > > Proposed Command: fuse writebuff
> > > > 
> > > > It would be good to provide some documentation links to the fuses that
> > > > you're wanting to deal with. What we have now works on a number of
> > > > diverse SoCs, even if for some cases it might be best to write a
> > > > script that's run rather than copy/paste things live. Any sort of new
> > > > mechanism needs to get feedback from users at other semiconductor
> > > > vendors to make sure it's generic enough for everyones needs. Thanks.
> > > > 
> > > 
> > > Hi Tom and Simon,
> > > 
> > > The buffer is not a text file. It is a structure in memory. The buffer is
> > > structured to contain all necessary information for the fuse programming
> > > process. This can include metadata, fuse programming data etc. The exact
> > > structure of the buffer can determined by the command_id, which provides
> > > flexibility for supporting different use cases. The memory buffer is
> > > typically prepared in user-space code or a script and loaded in memory
> > > before invoking the fuse writebuff command. It is not stored as a text file
> > > or any other file format, as the command operates directly on memory
> > > addresses.
> > > 
> > > Example of a buffer:
> > > 
> > > struct fuse_buffer {
> > >      struct fuse_mpkh smpkh;
> > >      struct fuse_msv msv;
> > >      struct fuse_key_cnt key_cnt;
> > >      u8 buffer_hash[64];
> > > };
> > > 
> > > This fuse_buffer struct will be loaded in memory containing all the
> > > necessary information for fuse programming.
> > > 
> > > struct fuse_mpkh {
> > >      u8 mpkh[64]; // public key hash
> > >      u8 bch[8];
> > >      u32 attributes; // read-protect, write-protect, override, active flag
> > >      u32 reserved[2];
> > > };
> > > struct fuse_msv {
> > >      u32 msv_with_bch; //model specific value
> > >      u32 attributes;
> > >      u32 reserved[2];
> > > };
> > > struct fuse_key_cnt {
> > >      u32 key_cnt; //key count
> > >      u32 attributes;
> > >      u32 reserved[2];
> > > };
> > > 
> > > -> eFUSE layout is abstract and isn't public as its programming and layout
> > > itself is security sensitive (it has authentication and decryption keys
> > > etc). So, fuse prog doesn't work as there is no "banks/offset" here.
> > > -> Platform Security Core running Secure SW exposes APIs through which these
> > > Keys and its attributes can be programmed. Whole content maybe encrypted for
> > > enhanced security on unsecure factory floor.
> > > -> There is a definite order in which these fields needs to be programmed.
> > > 
> > > Its possible to break the struct into 32bit values and send them across but
> > > we would end up with ~30 odd fuse prog cmds which is inefficient and error
> > > prone.
> > > It would be hard on secure core to also ensure correctness of operations
> > > against all sorts of silly errors (such of accidentally skipping a word or
> > > mess up ordering) which can render Silicon unusable.
> > > 
> > > So passing a opaque pointer with a command_id to Secure core is all that
> > > fuse cmd needs to do which is what writebuff supports.
> > > 
> > > This can be extended to any vendor; It's just an opaque pointer handoff. I
> > > see at least one other vendor do it in custom way:
> > > arch/arm/mach-imx/cmd_dek.c which could benefit from this new cmd fuse
> > > writebuff.
> > > 
> > > Here’s how the fuse writebuff command works in a typical flow:
> > > 1. Buffer Preparation: Vendors or developers create a complete buffer (e.g.,
> > > key.bin) containing all fuse programming data using vendor-specific scripts
> > > or tools and copied to SD card.
> > > 2. The buffer is loaded into memory using commands like:
> > > fatload mmc 1 0x80000000 key.bin
> > > 3. The fuse writebuff command passes the memory address (0x80000000) and
> > > command_id to the secure core:
> > > fuse writebuff <command_id> 0x80000000
> > > 4. The secure core receives the memory address as a pointer and validates,
> > > interprets it based on the command_id and then programs the fuses.
> > 
> > To summarize what we talked about on a call, I would like to see either:
> > 1) Work with arch/arm/mach-imx/cmd_dek.c and use that as the base of
> > some new generic command that deals with SoC-specific fuse
> > configurations that are handled via security processor.
> Hi Tom,
> 
> 1) I have looked at arch/arm/mach-imx/cmd_dek.c. The underlying
> implementation data structure is very specific to the vendor and how iMX
> devices are configured. The other vendors would also differ in their
> structures and SoC-specific fuse configurations, so I don't see a way to use
> this cmd_dek.c as the base and then abstract, create a new command out of
> it.
> 
> > OR
> > 2) Create a new command (that should be in cmd/ti/) for handling the K3
> > fuses, if we cannot make something abstract enough to handle this
> > concept on multiple vendors while having any sort of useful code re-use.
> 
> 2) In this case, I would like to add the fuse writebuff command for TI’s K3
> architecture in cmd/ti/k3_fuse.c. And the command will look like
> 
> fuse writebuff <command_id> <addr>
> 
> However, I would still like to place the fuse writebuff command in
> cmd/fuse.c as a generic interface because the parameters command_id and an
> opaque pointer handoff provides a mechanism for the secure core to interpret
> buffers differently based on vendor or use case.

This I guess is my confusion. If we can't abstract cmd_dek.c and the
underlying i.MX specific parts to be supported in "fuse writebuff ..."
what is the non-K3 (or better still, non-TI) abstraction for what you're
proposing?

-- 
Tom
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