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SubjectRe: [PATCHv4 06/10] arm64: add basic pointer authentication support
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Hi Mark,

On 03/05/18 14:20, Mark Rutland wrote:
> This patch adds basic support for pointer authentication, allowing
> userspace to make use of APIAKey. The kernel maintains an APIAKey value
> for each process (shared by all threads within), which is initialised to
> a random value at exec() time.
>
> To describe that address authentication instructions are available, the
> ID_AA64ISAR0.{APA,API} fields are exposed to userspace. A new hwcap,
> APIA, is added to describe that the kernel manages APIAKey.
>
> Instructions using other keys (APIBKey, APDAKey, APDBKey) are disabled,
> and will behave as NOPs. These may be made use of in future patches.
>
> No support is added for the generic key (APGAKey), though this cannot be
> trapped or made to behave as a NOP. Its presence is not advertised with
> a hwcap.
>
> Signed-off-by: Mark Rutland <mark.rutland@arm.com>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Ramana Radhakrishnan <ramana.radhakrishnan@arm.com>
> Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
> Cc: Will Deacon <will.deacon@arm.com>
> ---
> arch/arm64/include/asm/mmu.h | 5 +++
> arch/arm64/include/asm/mmu_context.h | 11 ++++-
> arch/arm64/include/asm/pointer_auth.h | 75 +++++++++++++++++++++++++++++++++++
> arch/arm64/include/uapi/asm/hwcap.h | 1 +
> arch/arm64/kernel/cpufeature.c | 9 +++++
> arch/arm64/kernel/cpuinfo.c | 1 +
> 6 files changed, 101 insertions(+), 1 deletion(-)
> create mode 100644 arch/arm64/include/asm/pointer_auth.h
>
> diff --git a/arch/arm64/include/asm/mmu.h b/arch/arm64/include/asm/mmu.h
> index dd320df0d026..f6480ea7b0d5 100644
> --- a/arch/arm64/include/asm/mmu.h
> +++ b/arch/arm64/include/asm/mmu.h
> @@ -25,10 +25,15 @@
>
> #ifndef __ASSEMBLY__
>
> +#include <asm/pointer_auth.h>
> +
> typedef struct {
> atomic64_t id;
> void *vdso;
> unsigned long flags;
> +#ifdef CONFIG_ARM64_PTR_AUTH
> + struct ptrauth_keys ptrauth_keys;
> +#endif
> } mm_context_t;
>
> /*
> diff --git a/arch/arm64/include/asm/mmu_context.h b/arch/arm64/include/asm/mmu_context.h
> index 39ec0b8a689e..83eadbc6b946 100644
> --- a/arch/arm64/include/asm/mmu_context.h
> +++ b/arch/arm64/include/asm/mmu_context.h
> @@ -168,7 +168,14 @@ static inline void cpu_replace_ttbr1(pgd_t *pgdp)
> #define destroy_context(mm) do { } while(0)
> void check_and_switch_context(struct mm_struct *mm, unsigned int cpu);
>
> -#define init_new_context(tsk,mm) ({ atomic64_set(&(mm)->context.id, 0); 0; })
> +static inline int init_new_context(struct task_struct *tsk,
> + struct mm_struct *mm)
> +{
> + atomic64_set(&mm->context.id, 0);
> + mm_ctx_ptrauth_init(&mm->context);
> +
> + return 0;
> +}>
> #ifdef CONFIG_ARM64_SW_TTBR0_PAN
> static inline void update_saved_ttbr0(struct task_struct *tsk,
> @@ -216,6 +223,8 @@ static inline void __switch_mm(struct mm_struct *next)
> return;
> }
>
> + mm_ctx_ptrauth_switch(&next->context);
> +
> check_and_switch_context(next, cpu);
> }

It seems you've removed arch_dup_mmap here (as Catalin suggested [1]),
but forgotten to move the key initialization from init_new_context to
arch_bprm_mm_init. In my tests I'm seeing child processes get different
keys than the parent after a fork().

Kristina

[1] https://lkml.org/lkml/2018/4/25/506

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