From: Huacai Chen <chenhuacai@kernel.org>
To: WANG Rui <r@hev.cc>
Cc: Ard Biesheuvel <ardb@kernel.org>, WANG Xuerui <kernel@xen0n.name>,
Ilias Apalodimas <ilias.apalodimas@linaro.org>,
loongarch@lists.linux.dev, linux-efi@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/3] efi/loongarch: Randomize kernel preferred address for KASLR
Date: Mon, 27 Apr 2026 21:27:35 +0800 [thread overview]
Message-ID: <CAAhV-H4CTAZT9pChSqv_j+ZT9VXUmYh7FoBS9gKmP95BzdPB-A@mail.gmail.com> (raw)
In-Reply-To: <20260427104721.47724-3-r@hev.cc>
Hi, Rui,
On Mon, Apr 27, 2026 at 6:47 PM WANG Rui <r@hev.cc> wrote:
>
> Introduce efi_get_kimg_kaslr_address() to compute the preferred
> kernel image address dynamically when CONFIG_RANDOMIZE_BASE is
> enabled. The function derives a random offset using EFI-provided
> randomness combined with the timer value, and constrains it within
> CONFIG_RANDOMIZE_BASE_MAX_OFFSET.
>
> Update EFI_KIMG_PREFERRED_ADDRESS to call this helper so that the
> EFI stub can select a randomized load address when KASLR is active,
> while preserving the original base address behavior when KASLR is
> disabled or nokaslr is specified.
>
> Signed-off-by: WANG Rui <r@hev.cc>
> ---
> arch/loongarch/Kconfig | 2 +-
> arch/loongarch/include/asm/efi.h | 4 +++-
> drivers/firmware/efi/libstub/loongarch.c | 16 ++++++++++++++++
> 3 files changed, 20 insertions(+), 2 deletions(-)
>
> diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
> index 3b042dbb2c41..a5afb70f73d9 100644
> --- a/arch/loongarch/Kconfig
> +++ b/arch/loongarch/Kconfig
> @@ -730,7 +730,7 @@ config RANDOMIZE_BASE
> config RANDOMIZE_BASE_MAX_OFFSET
> hex "Maximum KASLR offset" if EXPERT
> depends on RANDOMIZE_BASE
> - range 0x0 0x10000000
> + range 0x20000 0x10000000
Why modify this?
> default "0x01000000"
> help
> When KASLR is active, this provides the maximum offset that will
> diff --git a/arch/loongarch/include/asm/efi.h b/arch/loongarch/include/asm/efi.h
> index eddc8e79b3fa..f831320efd41 100644
> --- a/arch/loongarch/include/asm/efi.h
> +++ b/arch/loongarch/include/asm/efi.h
> @@ -30,6 +30,8 @@ static inline unsigned long efi_get_kimg_min_align(void)
> return SZ_2M;
> }
>
> -#define EFI_KIMG_PREFERRED_ADDRESS PHYSADDR(VMLINUX_LOAD_ADDRESS)
> +unsigned long efi_get_kimg_kaslr_address(void);
> +
> +#define EFI_KIMG_PREFERRED_ADDRESS efi_get_kimg_kaslr_address()
Can we reuse something in drivers/firmware/efi/libstub/kaslr.c?
>
> #endif /* _ASM_LOONGARCH_EFI_H */
> diff --git a/drivers/firmware/efi/libstub/loongarch.c b/drivers/firmware/efi/libstub/loongarch.c
> index 9825f5218137..df67ef8c68ab 100644
> --- a/drivers/firmware/efi/libstub/loongarch.c
> +++ b/drivers/firmware/efi/libstub/loongarch.c
> @@ -38,6 +38,22 @@ static efi_status_t exit_boot_func(struct efi_boot_memmap *map, void *priv)
> return EFI_SUCCESS;
> }
>
> +unsigned long efi_get_kimg_kaslr_address(void)
> +{
> + unsigned int random_offset = 0;
> +
> +#ifdef CONFIG_RANDOMIZE_BASE
> + if (!efi_nokaslr) {
> + efi_get_random_bytes(sizeof(random_offset), (u8 *)&random_offset);
> + random_offset ^= (rdtime_l() << 16);
Use get_cycles() then the first patch can be dropped.
Huacai
> + random_offset &= (CONFIG_RANDOMIZE_BASE_MAX_OFFSET - SZ_64K - 1);
> + random_offset = ALIGN(random_offset, SZ_64K) + SZ_64K;
> + }
> +#endif
> +
> + return PHYSADDR(VMLINUX_LOAD_ADDRESS) + random_offset;
> +}
> +
> unsigned long __weak kernel_entry_address(unsigned long kernel_addr,
> efi_loaded_image_t *image)
> {
> --
> 2.54.0
>
next prev parent reply other threads:[~2026-04-27 13:27 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-04-27 10:47 [PATCH 0/3] LoongArch: Move KASLR to EFI stub to avoid initrd overlap WANG Rui
2026-04-27 10:47 ` [PATCH 1/3] LoongArch: Allow rdtime_h() and rdtime_l() in 64-bit builds WANG Rui
2026-04-27 10:47 ` [PATCH 2/3] efi/loongarch: Randomize kernel preferred address for KASLR WANG Rui
2026-04-27 13:27 ` Huacai Chen [this message]
2026-04-27 15:29 ` hev
2026-04-27 10:47 ` [PATCH 3/3] LoongArch: Skip relocation-time KASLR if it has already been applied WANG Rui
2026-04-27 13:29 ` Huacai Chen
2026-04-27 15:30 ` hev
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