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Date: Fri, 29 Jan 2016 15:57:01 +0000
From: Matt Fleming <matt@...eblueprint.co.uk>
To: Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc: linux-arm-kernel@...ts.infradead.org,
kernel-hardening@...ts.openwall.com, will.deacon@....com,
catalin.marinas@....com, mark.rutland@....com,
leif.lindholm@...aro.org, keescook@...omium.org,
linux-kernel@...r.kernel.org, stuart.yoder@...escale.com,
bhupesh.sharma@...escale.com, arnd@...db.de, marc.zyngier@....com,
christoffer.dall@...aro.org, labbott@...oraproject.org
Subject: Re: [PATCH v4 22/22] arm64: efi: invoke EFI_RNG_PROTOCOL to supply
KASLR randomness
On Tue, 26 Jan, at 06:10:49PM, Ard Biesheuvel wrote:
> Since arm64 does not use a decompressor that supplies an execution
> environment where it is feasible to some extent to provide a source of
> randomness, the arm64 KASLR kernel depends on the bootloader to supply
> some random bits in the /chosen/kaslr-seed DT property upon kernel entry.
>
> On UEFI systems, we can use the EFI_RNG_PROTOCOL, if supplied, to obtain
> some random bits. At the same time, use it to randomize the offset of the
> kernel Image in physical memory.
>
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
> ---
> arch/arm64/Kconfig | 5 ++
> drivers/firmware/efi/libstub/arm-stub.c | 40 ++++++----
> drivers/firmware/efi/libstub/arm64-stub.c | 78 ++++++++++++++------
> drivers/firmware/efi/libstub/fdt.c | 9 +++
> 4 files changed, 97 insertions(+), 35 deletions(-)
[...]
> diff --git a/drivers/firmware/efi/libstub/fdt.c b/drivers/firmware/efi/libstub/fdt.c
> index cf7b7d46302a..04c9302b0ef1 100644
> --- a/drivers/firmware/efi/libstub/fdt.c
> +++ b/drivers/firmware/efi/libstub/fdt.c
> @@ -147,6 +147,15 @@ efi_status_t update_fdt(efi_system_table_t *sys_table, void *orig_fdt,
> if (status)
> goto fdt_set_fail;
>
> + if (IS_ENABLED(CONFIG_RANDOMIZE_BASE)) {
> + status = efi_get_random_bytes(sys_table, sizeof(fdt_val64),
> + (u8 *)&fdt_val64);
> + if (status == EFI_SUCCESS)
> + status = fdt_setprop(fdt, node, "kaslr-seed",
> + &fdt_val64, sizeof(fdt_val64));
> + else if (status != EFI_NOT_FOUND)
> + goto fdt_set_fail;
> + }
> return EFI_SUCCESS;
>
> fdt_set_fail:
I think you want to handle the case where fdt_setprop() fails. With
this new code you'll silently return EFI_SUCCESS even if you fail to
set "kaslr-seed".
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