From: Mark Rutland <mark.rutland@arm.com>
To: Ard Biesheuvel <ardb@kernel.org>
Cc: linux-arm-kernel@lists.infradead.org, will@kernel.org,
catalin.marinas@arm.com, Sami Tolvanen <samitolvanen@google.com>,
Kees Cook <keescook@chromium.org>
Subject: Re: [PATCH v2 1/2] arm64: Always load shadow stack pointer directly from the task struct
Date: Tue, 10 Jan 2023 14:55:31 +0000 [thread overview]
Message-ID: <Y718V9pF+UmcUYfX@FVFF77S0Q05N> (raw)
In-Reply-To: <20230109174800.3286265-2-ardb@kernel.org>
On Mon, Jan 09, 2023 at 06:47:59PM +0100, Ard Biesheuvel wrote:
> All occurrences of the scs_load macro load the value of the shadow call
> stack pointer from the task which is current at that point. So instead
> of taking a task struct register argument in the scs_load macro to
> specify the task struct to load from, let's always reference the current
> task directly. This should make it much harder to exploit any
> instruction sequences reloading the shadow call stack pointer register
> from memory.
>
> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Makes sense to me.
Acked-by: Mark Rutland <mark.rutland@arm.com>
Mark.
> ---
> arch/arm64/include/asm/scs.h | 7 ++++---
> arch/arm64/kernel/entry.S | 4 ++--
> arch/arm64/kernel/head.S | 2 +-
> 3 files changed, 7 insertions(+), 6 deletions(-)
>
> diff --git a/arch/arm64/include/asm/scs.h b/arch/arm64/include/asm/scs.h
> index ff7da1268a52ab79..13df982a080805e6 100644
> --- a/arch/arm64/include/asm/scs.h
> +++ b/arch/arm64/include/asm/scs.h
> @@ -10,15 +10,16 @@
> #ifdef CONFIG_SHADOW_CALL_STACK
> scs_sp .req x18
>
> - .macro scs_load tsk
> - ldr scs_sp, [\tsk, #TSK_TI_SCS_SP]
> + .macro scs_load_current
> + get_current_task scs_sp
> + ldr scs_sp, [scs_sp, #TSK_TI_SCS_SP]
> .endm
>
> .macro scs_save tsk
> str scs_sp, [\tsk, #TSK_TI_SCS_SP]
> .endm
> #else
> - .macro scs_load tsk
> + .macro scs_load_current
> .endm
>
> .macro scs_save tsk
> diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
> index 11cb99c4d298784d..546f7773238ea45d 100644
> --- a/arch/arm64/kernel/entry.S
> +++ b/arch/arm64/kernel/entry.S
> @@ -275,7 +275,7 @@ alternative_if ARM64_HAS_ADDRESS_AUTH
> alternative_else_nop_endif
> 1:
>
> - scs_load tsk
> + scs_load_current
> .else
> add x21, sp, #PT_REGS_SIZE
> get_current_task tsk
> @@ -848,7 +848,7 @@ SYM_FUNC_START(cpu_switch_to)
> msr sp_el0, x1
> ptrauth_keys_install_kernel x1, x8, x9, x10
> scs_save x0
> - scs_load x1
> + scs_load_current
> ret
> SYM_FUNC_END(cpu_switch_to)
> NOKPROBE(cpu_switch_to)
> diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
> index 952e17bd1c0b4f91..b9c1a506798ea315 100644
> --- a/arch/arm64/kernel/head.S
> +++ b/arch/arm64/kernel/head.S
> @@ -404,7 +404,7 @@ SYM_FUNC_END(create_kernel_mapping)
> stp xzr, xzr, [sp, #S_STACKFRAME]
> add x29, sp, #S_STACKFRAME
>
> - scs_load \tsk
> + scs_load_current
>
> adr_l \tmp1, __per_cpu_offset
> ldr w\tmp2, [\tsk, #TSK_TI_CPU]
> --
> 2.39.0
>
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next prev parent reply other threads:[~2023-01-10 14:56 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-09 17:47 [PATCH v2 0/2] arm64: harden shadow call stack pointer handling Ard Biesheuvel
2023-01-09 17:47 ` [PATCH v2 1/2] arm64: Always load shadow stack pointer directly from the task struct Ard Biesheuvel
2023-01-10 14:55 ` Mark Rutland [this message]
2023-01-12 22:18 ` Kees Cook
2023-01-09 17:48 ` [PATCH v2 2/2] arm64: Stash shadow stack pointer in the task struct on interrupt Ard Biesheuvel
2023-01-10 14:57 ` Mark Rutland
2023-01-12 22:18 ` Kees Cook
2023-01-20 16:59 ` [PATCH v2 0/2] arm64: harden shadow call stack pointer handling Catalin Marinas
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