On Wed, May 22, 2024 at 12:47 AM Michal Simek michal.simek@amd.com wrote:
On 5/21/24 22:59, 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.
If we have DM_RNG enabled populate this value automatically when fdt_chosen is called. We skip this if ARMV8_SEC_FIRMWARE_SUPPORT is enabled as it's implementation uses a different source of entropy that is not yet implemented as DM_RNG. We also skip this if MEASURED_BOOT is enabled as in that case any modifications to the dt will cause measured boot to fail (although there are many other places the dt is altered).
As this fdt node is added elsewhere create a library function and use it to deduplicate code. We will provide a parameter to specify the index of the rng device as well as a boolean to overwrite if present.
For our automatic injection, we will use the first rng device and not overwrite if already present with a non-zero value (which may have been populated by an earlier boot stage). This way if a board specific ft_board_setup() function wants to customize this behavior it can call fdt_kaslrseed with a rng device index of its choosing and set overwrite true.
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.
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.
Signed-off-by: Tim Harvey tharvey@gateworks.com Cc: Michal Simek michal.simek@amd.com Cc: Andy Yan andy.yan@rock-chips.com Cc: Akash Gajjar gajjar04akash@gmail.com Cc: Ilias Apalodimas ilias.apalodimas@linaro.org Cc: Simon Glass sjg@chromium.org Cc: Patrick Delaunay patrick.delaunay@foss.st.com Cc: Patrice Chotard patrice.chotard@foss.st.com Cc: Devarsh Thakkar devarsht@ti.com Cc: Heinrich Schuchardt xypron.glpk@gmx.de Cc: Hugo Villeneuve hvilleneuve@dimonoff.com Cc: Marek Vasut marex@denx.de Cc: Tom Rini trini@konsulko.com Cc: Chris Morgan macromorgan@hotmail.com
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
board/xilinx/common/board.c | 35 ------------------------- boot/fdt_support.c | 6 +++++ boot/pxe_utils.c | 35 ++----------------------- cmd/kaslrseed.c | 45 +++++--------------------------- include/kaslrseed.h | 19 ++++++++++++++ lib/Makefile | 1 + lib/kaslrseed.c | 51 +++++++++++++++++++++++++++++++++++++ 7 files changed, 85 insertions(+), 107 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));
one more thing here. Please also removed unused variables.
board/xilinx/common/board.c: In function 'ft_board_setup': board/xilinx/common/board.c:707:25: warning: unused variable 'ret' [-Wunused-variable] 707 | int nodeoffset, ret; | ^~~ board/xilinx/common/board.c:707:13: warning: unused variable 'nodeoffset' [-Wunused-variable] 707 | int nodeoffset, ret; | ^~~~~~~~~~ AS arch/arm/cpu/armv8/cache.o board/xilinx/common/board.c:706:12: warning: unused variable 'buf' [-Wunused-variable] 706 | u8 buf[MAX_RAND_SIZE]; | ^~~ board/xilinx/common/board.c:705:25: warning: unused variable 'dev' [-Wunused-variable] 705 | struct udevice *dev; | ^~~ board/xilinx/common/board.c:704:16: warning: unused variable 'n' [-Wunused-variable] 704 | size_t n = MAX_RAND_SIZE; | ^
Hi Michal,
Thanks... missed those. What defconfig are you building that gets to this codepath?
I'll send a v4 after another day or so for others to respond.
With these changes (and the previous response) do you have a rb or tested-by tag for me?
Best Regards,
Tim