[PATCH v2] fdt: automatically add /chosen/kaslr-seed if DM_RNG is enabled
Ilias Apalodimas
ilias.apalodimas at linaro.org
Tue May 21 20:58:29 CEST 2024
On Tue, 21 May 2024 at 21:05, Tim Harvey <tharvey at gateworks.com> wrote:
>
> On Tue, May 21, 2024 at 10:29 AM Ilias Apalodimas
> <ilias.apalodimas at linaro.org> wrote:
> >
> > On Tue, 21 May 2024 at 20:06, Tim Harvey <tharvey at gateworks.com> wrote:
> > >
> > > On Tue, May 21, 2024 at 9:54 AM Ilias Apalodimas
> > > <ilias.apalodimas at linaro.org> wrote:
> > > >
> > > > Hi Tim,
> > > >
> > > > On Tue, 21 May 2024 at 19:37, Tim Harvey <tharvey at gateworks.com> wrote:
> > > > >
> > > > > On Tue, May 21, 2024 at 5:05 AM Ilias Apalodimas
> > > > > <ilias.apalodimas at linaro.org> wrote:
> > > > > >
> > > > > > Hi Tim
> > > > > >
> > > > > > On Wed, 15 May 2024 at 23:50, Tim Harvey <tharvey at gateworks.com> 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.
> > > > > >
> > > > > > Since you'll send a v2, mind adding some description for UEFI on the
> > > > > > commit message?
> > > > > > efi_try_purge_kaslr_seed() has a comment of the behaviour
> > > > > >
> > > > >
> > > > > Hi Ilias,
> > > > >
> > > > > Ok, I will add the following to the commit log for clarity:
> > > > > Note that the Kernel's EFI STUB only relies on EFI_RNG_PROTOCOL for
> > > > > randomization and completely ignores the kaslr-seed for its own
> > > > > randomness needs (i.e the randomization of the physical placement of
> > > > > the kernel). It gets weeded out from the DTB that gets handed over via
> > > > > efi_install_fdt() as it would also mess up the measured boot DTB TPM
> > > > > measurements as well.
> > > > >
> > > > > Does the above mean that I don't need to worry about protecting the
> > > > > call to fdt_kaslrseed() with a check for MEASURED BOOT as
> > > > > efi_install_fdt/efi_try_purge_kaslr_seed always gets called in that
> > > > > case?
> > > >
> > > > There are 2 ways to do measured boot. One is via the bootm command and
> > > > the other is via the EFI protocols.
> > > > CONFIG_MEASURED_BOOT only applies to bootm.
> > > > OTOH kaslr-seed might still have value if EFI_RNG is disabled, even
> > > > when booting with EFI, since the kernel will randomize the virtual
> > > > placement if it finds that.
> > > >
> > > > But in any case, a kaslr-seed entry can't be present in the DTB if you
> > > > plan to measure it.
> > >
> > > ok, sounds like I need to use:
> > >
> > > if (IS_ENABLED(CONFIG_DM_RNG) &&
> > > !IS_ENABLED(ARMV8_SEC_FIRMWARE_SUPPORT)) &&
> > > !IS_ENABLED(CONFIG_MEASURED_BOOT) {
> > > fdt_kaslrseed...
> > > }
> > >
> >
> > Can't we measure the DT *before* adding the kaslr-seed?
> >
>
> You tell me... I'm deferring to you regarding what is needed for this
> patch for measured boot.
>
> What changes do I need to make and why?
Ok, thinking it a bit more we can't reliably measure the DT before a
kaslr-seed gets injected, simply because an earlier stage bootloader
might have injected it.... That's why we had a config option (and at
least we mention it in aa2d3945ce6df43903d76cadde1c0669d6d5d43b but
not in great detail).
However, for a user that's far from ideal since he needs to be aware
of those details before enabling measurements for the DT.
Looking at our EFI code we *try* to purge the kaslr-seed before
measuring the DT, but that doesn't guarantee it won't be there -- it
will be purged only if EFI_RNG is installed. But that only happens if
you have an RNG available.
To make things even worse, the kaslr-seed is not the only source of
randomness when measuring a DT, a mac address entry for example would
have the same effect.
On top of all these EFI code measures on PCR0 and bootm on PCR8. The
reason for that is that although the EFI spec has no guidance on
measuring a DT, it does have for ACPI and it uses PCR0 [0].
I think all these should be fixed and at least documented properly for
now, but that's unfair to you since it's irrelevant to what your patch
is trying to fix ...
As for recommendations, I haven't looked into bootm code for quite
some time. Can we inject kaslr-seed after we measure it? If yes, then
do that and let's add a comment about the current mess...
[0] https://trustedcomputinggroup.org/wp-content/uploads/TCG_PCClient_PFP_r1p05_v23_pub.pdf
3.3.4.1 PCR[0] – SRTM, POST BIOS, and Embedded Drivers
>
> Best Regards,
>
> Tim
>
> > Cheers
> > /Ilias
> > > Thanks,
> > >
> > > I'll send a v3 hopefully later today.
> > >
> > > Tim
> > >
> > > >
> > > > Cheers
> > > > /Ilias
> > > >
> > > > >
> > > > > Best Regards,
> > > > >
> > > > > Tim
> > > > >
> > > > > > Thanks
> > > > > > /Ilias
> > > > > > >
> > > > > > > If we have DM_RNG enabled populate this value automatically when
> > > > > > > fdt_chosen is called unless ARMV8_SEC_FIRMWARE_SUPPORT is enabled as
> > > > > > > it's implementation uses a different source of entropy.
> > > > > > >
> > > > > > > As this fdt node is added elsewhere create a library function and
> > > > > > > use it to deduplicate code.
> > > > > > >
> > > > > > > Note that the kalsrseed command (CMD_KASLRSEED) is likely pointless now
> > > > > > > but left in place in case boot scripts exist that rely on this command
> > > > > > > existing and returning success. An informational message is printed to
> > > > > > > alert users of this command that it is likely no longer needed.
> > > > > > >
> > > > > > > Signed-off-by: Tim Harvey <tharvey at gateworks.com>
> > > > > > > ---
> > > > > > > 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
> > > > > > > ---
> > > > > > > board/xilinx/common/board.c | 35 -----------------------------
> > > > > > > boot/fdt_support.c | 10 +++++++++
> > > > > > > boot/pxe_utils.c | 35 +++--------------------------
> > > > > > > cmd/kaslrseed.c | 45 ++++++-------------------------------
> > > > > > > include/kaslrseed.h | 17 ++++++++++++++
> > > > > > > lib/Makefile | 1 +
> > > > > > > lib/kaslrseed.c | 34 ++++++++++++++++++++++++++++
> > > > > > > 7 files changed, 72 insertions(+), 105 deletions(-)
> > > > > > > create mode 100644 include/kaslrseed.h
> > > > > > > create mode 100644 lib/kaslrseed.c
> > > > > > >
> > > > > > > diff --git a/board/xilinx/common/board.c b/board/xilinx/common/board.c
> > > > > > > index 30a81376ac41..f741e8957818 100644
> > > > > > > --- a/board/xilinx/common/board.c
> > > > > > > +++ b/board/xilinx/common/board.c
> > > > > > > @@ -713,41 +713,6 @@ int ft_board_setup(void *blob, struct bd_info *bd)
> > > > > > > if (IS_ENABLED(CONFIG_FDT_FIXUP_PARTITIONS) && IS_ENABLED(CONFIG_NAND_ZYNQ))
> > > > > > > fdt_fixup_mtdparts(blob, nodes, ARRAY_SIZE(nodes));
> > > > > > >
> > > > > > > - if (uclass_get_device(UCLASS_RNG, 0, &dev) || !dev) {
> > > > > > > - debug("No RNG device\n");
> > > > > > > - return 0;
> > > > > > > - }
> > > > > > > -
> > > > > > > - if (dm_rng_read(dev, buf, n)) {
> > > > > > > - debug("Reading RNG failed\n");
> > > > > > > - return 0;
> > > > > > > - }
> > > > > > > -
> > > > > > > - if (!blob) {
> > > > > > > - debug("No FDT memory address configured. Please configure\n"
> > > > > > > - "the FDT address via \"fdt addr <address>\" command.\n"
> > > > > > > - "Aborting!\n");
> > > > > > > - return 0;
> > > > > > > - }
> > > > > > > -
> > > > > > > - ret = fdt_check_header(blob);
> > > > > > > - if (ret < 0) {
> > > > > > > - debug("fdt_chosen: %s\n", fdt_strerror(ret));
> > > > > > > - return ret;
> > > > > > > - }
> > > > > > > -
> > > > > > > - nodeoffset = fdt_find_or_add_subnode(blob, 0, "chosen");
> > > > > > > - if (nodeoffset < 0) {
> > > > > > > - debug("Reading chosen node failed\n");
> > > > > > > - return nodeoffset;
> > > > > > > - }
> > > > > > > -
> > > > > > > - ret = fdt_setprop(blob, nodeoffset, "kaslr-seed", buf, sizeof(buf));
> > > > > > > - if (ret < 0) {
> > > > > > > - debug("Unable to set kaslr-seed on chosen node: %s\n", fdt_strerror(ret));
> > > > > > > - return ret;
> > > > > > > - }
> > > > > > > -
> > > > > > > return 0;
> > > > > > > }
> > > > > > > #endif
> > > > > > > diff --git a/boot/fdt_support.c b/boot/fdt_support.c
> > > > > > > index 874ca4d6f5af..3455d60d69dc 100644
> > > > > > > --- a/boot/fdt_support.c
> > > > > > > +++ b/boot/fdt_support.c
> > > > > > > @@ -8,6 +8,7 @@
> > > > > > >
> > > > > > > #include <abuf.h>
> > > > > > > #include <env.h>
> > > > > > > +#include <kaslrseed.h>
> > > > > > > #include <log.h>
> > > > > > > #include <mapmem.h>
> > > > > > > #include <net.h>
> > > > > > > @@ -300,6 +301,15 @@ int fdt_chosen(void *fdt)
> > > > > > > if (nodeoffset < 0)
> > > > > > > return nodeoffset;
> > > > > > >
> > > > > > > + if (IS_ENABLED(CONFIG_DM_RNG) && !IS_ENABLED(ARMV8_SEC_FIRMWARE_SUPPORT)) {
> > > > > > > + err = fdt_kaslrseed(fdt);
> > > > > > > + if (err) {
> > > > > > > + printf("WARNING: could not set kaslr-seed %s.\n",
> > > > > > > + fdt_strerror(err));
> > > > > > > + return err;
> > > > > > > + }
> > > > > > > + }
> > > > > > > +
> > > > > > > if (IS_ENABLED(CONFIG_BOARD_RNG_SEED) && !board_rng_seed(&buf)) {
> > > > > > > err = fdt_setprop(fdt, nodeoffset, "rng-seed",
> > > > > > > abuf_data(&buf), abuf_size(&buf));
> > > > > > > diff --git a/boot/pxe_utils.c b/boot/pxe_utils.c
> > > > > > > index 4b22bb6f525a..8d70233fc08d 100644
> > > > > > > --- a/boot/pxe_utils.c
> > > > > > > +++ b/boot/pxe_utils.c
> > > > > > > @@ -8,6 +8,7 @@
> > > > > > > #include <dm.h>
> > > > > > > #include <env.h>
> > > > > > > #include <image.h>
> > > > > > > +#include <kaslrseed.h>
> > > > > > > #include <log.h>
> > > > > > > #include <malloc.h>
> > > > > > > #include <mapmem.h>
> > > > > > > @@ -323,10 +324,6 @@ static void label_boot_kaslrseed(void)
> > > > > > > #if CONFIG_IS_ENABLED(DM_RNG)
> > > > > > > ulong fdt_addr;
> > > > > > > struct fdt_header *working_fdt;
> > > > > > > - size_t n = 0x8;
> > > > > > > - struct udevice *dev;
> > > > > > > - u64 *buf;
> > > > > > > - int nodeoffset;
> > > > > > > int err;
> > > > > > >
> > > > > > > /* Get the main fdt and map it */
> > > > > > > @@ -342,35 +339,9 @@ static void label_boot_kaslrseed(void)
> > > > > > > if (err <= 0)
> > > > > > > return;
> > > > > > >
> > > > > > > - if (uclass_get_device(UCLASS_RNG, 0, &dev) || !dev) {
> > > > > > > - printf("No RNG device\n");
> > > > > > > - return;
> > > > > > > - }
> > > > > > > -
> > > > > > > - nodeoffset = fdt_find_or_add_subnode(working_fdt, 0, "chosen");
> > > > > > > - if (nodeoffset < 0) {
> > > > > > > - printf("Reading chosen node failed\n");
> > > > > > > - return;
> > > > > > > - }
> > > > > > > -
> > > > > > > - buf = malloc(n);
> > > > > > > - if (!buf) {
> > > > > > > - printf("Out of memory\n");
> > > > > > > - return;
> > > > > > > - }
> > > > > > > -
> > > > > > > - if (dm_rng_read(dev, buf, n)) {
> > > > > > > - printf("Reading RNG failed\n");
> > > > > > > - goto err;
> > > > > > > - }
> > > > > > > -
> > > > > > > - err = fdt_setprop(working_fdt, nodeoffset, "kaslr-seed", buf, sizeof(buf));
> > > > > > > - if (err < 0) {
> > > > > > > + err = fdt_kaslrseed(working_fdt);
> > > > > > > + if (err < 0)
> > > > > > > printf("Unable to set kaslr-seed on chosen node: %s\n", fdt_strerror(err));
> > > > > > > - goto err;
> > > > > > > - }
> > > > > > > -err:
> > > > > > > - free(buf);
> > > > > > > #endif
> > > > > > > return;
> > > > > > > }
> > > > > > > diff --git a/cmd/kaslrseed.c b/cmd/kaslrseed.c
> > > > > > > index e0d3c7fe7489..ea5c07d729cf 100644
> > > > > > > --- a/cmd/kaslrseed.c
> > > > > > > +++ b/cmd/kaslrseed.c
> > > > > > > @@ -9,33 +9,16 @@
> > > > > > > #include <command.h>
> > > > > > > #include <dm.h>
> > > > > > > #include <hexdump.h>
> > > > > > > +#include <kaslrseed.h>
> > > > > > > #include <malloc.h>
> > > > > > > #include <rng.h>
> > > > > > > #include <fdt_support.h>
> > > > > > >
> > > > > > > static int do_kaslr_seed(struct cmd_tbl *cmdtp, int flag, int argc, char *const argv[])
> > > > > > > {
> > > > > > > - size_t n = 0x8;
> > > > > > > - struct udevice *dev;
> > > > > > > - u64 *buf;
> > > > > > > - int nodeoffset;
> > > > > > > - int ret = CMD_RET_SUCCESS;
> > > > > > > + int err;
> > > > > > >
> > > > > > > - if (uclass_get_device(UCLASS_RNG, 0, &dev) || !dev) {
> > > > > > > - printf("No RNG device\n");
> > > > > > > - return CMD_RET_FAILURE;
> > > > > > > - }
> > > > > > > -
> > > > > > > - buf = malloc(n);
> > > > > > > - if (!buf) {
> > > > > > > - printf("Out of memory\n");
> > > > > > > - return CMD_RET_FAILURE;
> > > > > > > - }
> > > > > > > -
> > > > > > > - if (dm_rng_read(dev, buf, n)) {
> > > > > > > - printf("Reading RNG failed\n");
> > > > > > > - return CMD_RET_FAILURE;
> > > > > > > - }
> > > > > > > + printf("Notice: a /chosen/kaslr-seed is automatically added to the device-tree when booted via booti/bootm/bootz therefore using this command is likely no longer needed");
> > > > > > >
> > > > > > > if (!working_fdt) {
> > > > > > > printf("No FDT memory address configured. Please configure\n"
> > > > > > > @@ -44,27 +27,13 @@ static int do_kaslr_seed(struct cmd_tbl *cmdtp, int flag, int argc, char *const
> > > > > > > return CMD_RET_FAILURE;
> > > > > > > }
> > > > > > >
> > > > > > > - ret = fdt_check_header(working_fdt);
> > > > > > > - if (ret < 0) {
> > > > > > > - printf("fdt_chosen: %s\n", fdt_strerror(ret));
> > > > > > > + err = fdt_kaslrseed(working_fdt);
> > > > > > > + if (err < 0) {
> > > > > > > + printf("Unable to set kaslr-seed on chosen node: %s\n", fdt_strerror(err));
> > > > > > > return CMD_RET_FAILURE;
> > > > > > > }
> > > > > > >
> > > > > > > - nodeoffset = fdt_find_or_add_subnode(working_fdt, 0, "chosen");
> > > > > > > - if (nodeoffset < 0) {
> > > > > > > - printf("Reading chosen node failed\n");
> > > > > > > - return CMD_RET_FAILURE;
> > > > > > > - }
> > > > > > > -
> > > > > > > - ret = fdt_setprop(working_fdt, nodeoffset, "kaslr-seed", buf, sizeof(buf));
> > > > > > > - if (ret < 0) {
> > > > > > > - printf("Unable to set kaslr-seed on chosen node: %s\n", fdt_strerror(ret));
> > > > > > > - return CMD_RET_FAILURE;
> > > > > > > - }
> > > > > > > -
> > > > > > > - free(buf);
> > > > > > > -
> > > > > > > - return ret;
> > > > > > > + return CMD_RET_SUCCESS;
> > > > > > > }
> > > > > > >
> > > > > > > U_BOOT_LONGHELP(kaslrseed,
> > > > > > > diff --git a/include/kaslrseed.h b/include/kaslrseed.h
> > > > > > > new file mode 100644
> > > > > > > index 000000000000..3fe82f418acf
> > > > > > > --- /dev/null
> > > > > > > +++ b/include/kaslrseed.h
> > > > > > > @@ -0,0 +1,17 @@
> > > > > > > +/* SPDX-License-Identifier: GPL-2.0+ */
> > > > > > > +/*
> > > > > > > + * Copyright 2024 Tim Harvey <tharvey at gateworks.com>
> > > > > > > + */
> > > > > > > +
> > > > > > > +#if !defined _KASLRSEED_H_
> > > > > > > +#define _KASLRSEED_H_
> > > > > > > +
> > > > > > > +/**
> > > > > > > + * fdt_kaslrseed() - create a 'kaslr-seed' node in chosen
> > > > > > > + *
> > > > > > > + * @blob: fdt blob
> > > > > > > + * Return: 0 if OK, -ve on error
> > > > > > > + */
> > > > > > > +int fdt_kaslrseed(void *blob);
> > > > > > > +
> > > > > > > +#endif /* _KASLRSEED_H_ */
> > > > > > > diff --git a/lib/Makefile b/lib/Makefile
> > > > > > > index 2a76acf100d0..20a0242055fa 100644
> > > > > > > --- a/lib/Makefile
> > > > > > > +++ b/lib/Makefile
> > > > > > > @@ -149,6 +149,7 @@ obj-y += date.o
> > > > > > > obj-y += rtc-lib.o
> > > > > > > obj-$(CONFIG_LIB_ELF) += elf.o
> > > > > > >
> > > > > > > +obj-$(CONFIG_DM_RNG) += kaslrseed.o
> > > > > > > obj-$(CONFIG_$(SPL_TPL_)SEMIHOSTING) += semihosting.o
> > > > > > >
> > > > > > > #
> > > > > > > diff --git a/lib/kaslrseed.c b/lib/kaslrseed.c
> > > > > > > new file mode 100644
> > > > > > > index 000000000000..ad06bee2b88d
> > > > > > > --- /dev/null
> > > > > > > +++ b/lib/kaslrseed.c
> > > > > > > @@ -0,0 +1,34 @@
> > > > > > > +// SPDX-License-Identifier: GPL-2.0+
> > > > > > > +/*
> > > > > > > + * Copyright 2024 Tim Harvey <tharvey at gateworks.com>
> > > > > > > + */
> > > > > > > +#include <dm.h>
> > > > > > > +#include <rng.h>
> > > > > > > +#include <fdt_support.h>
> > > > > > > +
> > > > > > > +int fdt_kaslrseed(void *fdt)
> > > > > > > +{
> > > > > > > + struct udevice *dev;
> > > > > > > + int nodeoffset;
> > > > > > > + u64 data;
> > > > > > > + int err;
> > > > > > > +
> > > > > > > + err = fdt_check_header(fdt);
> > > > > > > + if (err < 0)
> > > > > > > + return err;
> > > > > > > +
> > > > > > > + /* find or create "/chosen" node. */
> > > > > > > + nodeoffset = fdt_find_or_add_subnode(fdt, 0, "chosen");
> > > > > > > + if (nodeoffset < 0)
> > > > > > > + return nodeoffset;
> > > > > > > +
> > > > > > > + err = uclass_get_device(UCLASS_RNG, 0, &dev);
> > > > > > > + if (!err)
> > > > > > > + err = dm_rng_read(dev, &data, sizeof(data));
> > > > > > > + if (!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;
> > > > > > > +}
> > > > > > > --
> > > > > > > 2.25.1
> > > > > > >
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