[PATCH v7 1/4] Add fdt_kaslrseed function to add kaslr-seed to chosen node

[Caleb Connolly]

On 24/06/2024 17:47, Tim Harvey wrote:
> On Thu, Jun 20, 2024 at 6:58 AM Caleb Connolly
> <caleb.connolly at linaro.org> wrote:
>>
>> Hi Tim,
>>
>> On 18/06/2024 23:06, Tim Harvey wrote:
>>> If RANDOMIZE_BASE is enabled in the Linux kernel instructing it to
>>> randomize the virtual address at which the kernel image is loaded, it
>>> expects entropy to be provided by the bootloader by populating
>>> /chosen/kaslr-seed with a 64-bit value from source of entropy at boot.
>>>
>>> Add a fdt_kaslrseed function to accommodate this allowing an existing
>>> node to be overwritten if present. For now use the first rng device
>>> but it would be good to enhance this in the future to allow some sort
>>> of selection or policy in choosing the rng device used.
>>>
>>> Signed-off-by: Tim Harvey <tharvey at gateworks.com>
>>> Reviewed-by: Simon Glass <sjg at chromium.org>
>>> Cc: Michal Simek <michal.simek at amd.com>
>>> Cc: Andy Yan <andy.yan at rock-chips.com>
>>> Cc: Akash Gajjar <gajjar04akash at gmail.com>
>>> Cc: Ilias Apalodimas <ilias.apalodimas at linaro.org>
>>> Cc: Simon Glass <sjg at chromium.org>
>>> Cc: Patrick Delaunay <patrick.delaunay at foss.st.com>
>>> Cc: Patrice Chotard <patrice.chotard at foss.st.com>
>>> Cc: Devarsh Thakkar <devarsht at ti.com>
>>> Cc: Heinrich Schuchardt <xypron.glpk at gmx.de>
>>> Cc: Hugo Villeneuve <hvilleneuve at dimonoff.com>
>>> Cc: Marek Vasut <marex at denx.de>
>>> Cc: Tom Rini <trini at konsulko.com>
>>> Cc: Chris Morgan <macromorgan at hotmail.com>
>>> ---
>>> v6:
>>>    - collected tags
>>> v5:
>>>    - move function to boot/fdt_support.c
>>>    - remove ability to select rng index and note in the commit log
>>>      something like this as a future enhancement.
>>>    - fixed typo in commit message s/it's/its/
>>>    - use cmd_process_error per Michal's suggestion
>>> v4:
>>>    - add missing /n to notice in kaslrseed cmd
>>>    - combine ints in declaration
>>>    - remove unused vars from board/xilinx/common/board.c ft_board_setup
>>> v3:
>>>    - skip if CONFIG_MEASURED_BOOT
>>>    - fix skip for CONFIG_ARMV8_SEC_FIRMWARE_SUPPORT
>>>    - pass in rng index and bool to specify overwrite
>>>    - remove duplicate error strings printed outside of fdt_kaslrseed
>>>    - added note to commit log about how EFI STUB weeds out kalsr-seed
>>> v2:
>>>    - fix typo in commit msg
>>>    - use stack for seed to avoid unecessary malloc/free
>>>    - move to a library function and deduplicate code by using it
>>>      elsewhere
>>> ---
>>>    boot/fdt_support.c    | 44 +++++++++++++++++++++++++++++++++++++++++++
>>>    include/fdt_support.h | 10 ++++++++++
>>>    2 files changed, 54 insertions(+)
>>>
>>> diff --git a/boot/fdt_support.c b/boot/fdt_support.c
>>> index 2bd80a9dfb18..b1b2679dea0c 100644
>>> --- a/boot/fdt_support.c
>>> +++ b/boot/fdt_support.c
>>> @@ -7,12 +7,15 @@
>>>     */
>>>
>>>    #include <common.h>
>>> +#include <dm.h>
>>>    #include <abuf.h>
>>>    #include <env.h>
>>>    #include <log.h>
>>>    #include <mapmem.h>
>>>    #include <net.h>
>>> +#include <rng.h>
>>>    #include <stdio_dev.h>
>>> +#include <dm/device_compat.h>
>>>    #include <dm/ofnode.h>
>>>    #include <linux/ctype.h>
>>>    #include <linux/types.h>
>>> @@ -274,6 +277,47 @@ int fdt_initrd(void *fdt, ulong initrd_start, ulong initrd_end)
>>>        return 0;
>>>    }
>>>
>>> +int fdt_kaslrseed(void *fdt, bool overwrite)
>>> +{
>>> +     int len, err, nodeoffset;
>>> +     struct udevice *dev;
>>> +     const u64 *orig;
>>> +     u64 data = 0;
>>> +
>>> +     err = fdt_check_header(fdt);
>>> +     if (err < 0)
>>> +             return err;
>>
>> All the paths that call fdt_kaslrseed() call fdt_check_header()
>> beforehand, I think it's safe to drop this.
> 
> Hi Caleb,
> 
> The do_kaslr_seed path does not check for this and instead passes
> working_fdt - perhaps your point is still valid if working_fdt is
> guaranteed to always be a valid fdt?
> 
>>> +
>>> +     /* find or create "/chosen" node. */
>>> +     nodeoffset = fdt_find_or_add_subnode(fdt, 0, "chosen");
>>> +     if (nodeoffset < 0)
>>> +             return nodeoffset;
>>
>> Arguably, this shouldn't be the responsibility of this function, maybe
>> it would be better to error our here?
> 
> I'm not sure what your point is here... it is erroring out.

Hi Tim,

On a re-read, I'm honestly not sure what I was getting at here. I was 
under the impression that were were doing fdt_check_header() multiple 
times on the same fdt, but if that's not the case then this is of course 
fine.

Regarding the chosen node, clearly something went amiss between brain 
and keyboard there.

Sorry if I delayed this patch series! Looking forward to having it in.

Reviewed-by: Caleb Connolly <caleb.connolly at linaro.org>

Thanks and regards,
> 
> Best Regards,
> 
> Tim
> 
>>> +
>>> +     /* return without error if we are not overwriting and existing non-zero node */
>>> +     orig = fdt_getprop(fdt, nodeoffset, "kaslr-seed", &len);
>>> +     if (orig && len == sizeof(*orig))
>>> +             data = fdt64_to_cpu(*orig);
>>> +     if (data && !overwrite) {
>>> +             debug("not overwriting existing kaslr-seed\n");
>>> +             return 0;
>>> +     }
>>> +     err = uclass_get_device(UCLASS_RNG, 0, &dev);
>>> +     if (err) {
>>> +             printf("No RNG device\n");
>>> +             return err;
>>> +     }
>>> +     err = dm_rng_read(dev, &data, sizeof(data));
>>> +     if (err) {
>>> +             dev_err(dev, "dm_rng_read failed: %d\n", err);
>>> +             return err;
>>> +     }
>>> +     err = fdt_setprop(fdt, nodeoffset, "kaslr-seed", &data, sizeof(data));
>>> +     if (err < 0)
>>> +             printf("WARNING: could not set kaslr-seed %s.\n", fdt_strerror(err));
>>> +
>>> +     return err;
>>> +}
>>> +
>>>    /**
>>>     * board_fdt_chosen_bootargs - boards may override this function to use
>>>     *                             alternative kernel command line arguments
>>> diff --git a/include/fdt_support.h b/include/fdt_support.h
>>> index 4b71b8948d99..741e2360c224 100644
>>> --- a/include/fdt_support.h
>>> +++ b/include/fdt_support.h
>>> @@ -463,4 +463,14 @@ void fdt_fixup_board_enet(void *blob);
>>>    #ifdef CONFIG_CMD_PSTORE
>>>    void fdt_fixup_pstore(void *blob);
>>>    #endif
>>> +
>>> +/**
>>> + * fdt_kaslrseed() - create a 'kaslr-seed' node in chosen
>>> + *
>>> + * @blob:    fdt blob
>>> + * @overwrite:       do not overwrite existing non-zero node unless true
>>> + * Return:   0 if OK, -ve on error
>>> + */
>>> +int fdt_kaslrseed(void *blob, bool overwrite);
>>> +
>>>    #endif /* ifndef __FDT_SUPPORT_H */
>>
>> --
>> // Caleb (they/them)

-- 
// Caleb (they/them)