[PATCH v1 1/2] riscv: abstract envcfg CSR

[Deepak Gupta]

Some issues in workflow. Patches didn't come out separately.

Ignore this.

On Tue, Dec 12, 2023 at 3:43 PM Deepak Gupta <debug at rivosinc.com> wrote:
>
> This patch abstracts envcfg CSR in kernel (as is done for other homonyn
> CSRs). CSR_ENVCFG is used as alias for CSR_SENVCFG or CSR_MENVCFG depending
> on how kernel is compiled.
>
> Additionally it changes CBZE enabling to start using CSR_ENVCFG instead of
> CSR_SENVCFG.
>
> Signed-off-by: Deepak Gupta <debug at rivosinc.com>
> ---
>  arch/riscv/include/asm/csr.h   | 2 ++
>  arch/riscv/kernel/cpufeature.c | 2 +-
>  2 files changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/arch/riscv/include/asm/csr.h b/arch/riscv/include/asm/csr.h
> index 306a19a5509c..b3400517b0a9 100644
> --- a/arch/riscv/include/asm/csr.h
> +++ b/arch/riscv/include/asm/csr.h
> @@ -415,6 +415,7 @@
>  # define CSR_STATUS    CSR_MSTATUS
>  # define CSR_IE                CSR_MIE
>  # define CSR_TVEC      CSR_MTVEC
> +# define CSR_ENVCFG CSR_MENVCFG
>  # define CSR_SCRATCH   CSR_MSCRATCH
>  # define CSR_EPC       CSR_MEPC
>  # define CSR_CAUSE     CSR_MCAUSE
> @@ -439,6 +440,7 @@
>  # define CSR_STATUS    CSR_SSTATUS
>  # define CSR_IE                CSR_SIE
>  # define CSR_TVEC      CSR_STVEC
> +# define CSR_ENVCFG CSR_SENVCFG
>  # define CSR_SCRATCH   CSR_SSCRATCH
>  # define CSR_EPC       CSR_SEPC
>  # define CSR_CAUSE     CSR_SCAUSE
> diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
> index b3785ffc1570..98623393fd1f 100644
> --- a/arch/riscv/kernel/cpufeature.c
> +++ b/arch/riscv/kernel/cpufeature.c
> @@ -725,7 +725,7 @@ arch_initcall(check_unaligned_access_all_cpus);
>  void riscv_user_isa_enable(void)
>  {
>         if (riscv_cpu_has_extension_unlikely(smp_processor_id(), RISCV_ISA_EXT_ZICBOZ))
> -               csr_set(CSR_SENVCFG, ENVCFG_CBZE);
> +               csr_set(CSR_ENVCFG, ENVCFG_CBZE);
>  }
>
>  #ifdef CONFIG_RISCV_ALTERNATIVE
> --
> 2.43.0
>
>
> From 2ad5b91bda97f6dbc9f48a2e0e8c6eae5b8452ca Mon Sep 17 00:00:00 2001
> From: Deepak Gupta <debug at rivosinc.com>
> Date: Tue, 12 Dec 2023 14:28:59 -0800
> Subject: [PATCH v1 2/2] riscv: envcfg save and restore on trap entry/exit
>
> envcfg CSR defines enabling bits for cache management instructions and soon
> will control enabling for control flow integrity and pointer masking features.
>
> Control flow integrity and pointer masking features need to be enabled on per
> thread basis. Additionally, I believe cache management instructions need to be
> enabled on per thread basis. As an example a seccomped task on riscv may be
> restricted to not use cache management instructions
>
> This patch creates a place holder for envcfg CSR in `thread_info` and adds
> logic to save and restore on trap entry and exits. This allows such isa feature
> to be enabled on per thread basis.
>
> Signed-off-by: Deepak Gupta <debug at rivosinc.com>
> ---
>  arch/riscv/include/asm/thread_info.h | 1 +
>  arch/riscv/kernel/asm-offsets.c      | 1 +
>  arch/riscv/kernel/entry.S            | 6 ++++++
>  3 files changed, 8 insertions(+)
>
> diff --git a/arch/riscv/include/asm/thread_info.h b/arch/riscv/include/asm/thread_info.h
> index 574779900bfb..320bc899a63b 100644
> --- a/arch/riscv/include/asm/thread_info.h
> +++ b/arch/riscv/include/asm/thread_info.h
> @@ -57,6 +57,7 @@ struct thread_info {
>         long                    user_sp;        /* User stack pointer */
>         int                     cpu;
>         unsigned long           syscall_work;   /* SYSCALL_WORK_ flags */
> +       unsigned long envcfg;
>  #ifdef CONFIG_SHADOW_CALL_STACK
>         void                    *scs_base;
>         void                    *scs_sp;
> diff --git a/arch/riscv/kernel/asm-offsets.c b/arch/riscv/kernel/asm-offsets.c
> index a03129f40c46..cdd8f095c30c 100644
> --- a/arch/riscv/kernel/asm-offsets.c
> +++ b/arch/riscv/kernel/asm-offsets.c
> @@ -39,6 +39,7 @@ void asm_offsets(void)
>         OFFSET(TASK_TI_PREEMPT_COUNT, task_struct, thread_info.preempt_count);
>         OFFSET(TASK_TI_KERNEL_SP, task_struct, thread_info.kernel_sp);
>         OFFSET(TASK_TI_USER_SP, task_struct, thread_info.user_sp);
> +       OFFSET(TASK_TI_ENVCFG, task_struct, thread_info.envcfg);
>  #ifdef CONFIG_SHADOW_CALL_STACK
>         OFFSET(TASK_TI_SCS_SP, task_struct, thread_info.scs_sp);
>  #endif
> diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S
> index 54ca4564a926..a1d87013f15a 100644
> --- a/arch/riscv/kernel/entry.S
> +++ b/arch/riscv/kernel/entry.S
> @@ -64,12 +64,14 @@ SYM_CODE_START(handle_exception)
>         csrr s3, CSR_TVAL
>         csrr s4, CSR_CAUSE
>         csrr s5, CSR_SCRATCH
> +       csrr s6, CSR_ENVCFG
>         REG_S s0, PT_SP(sp)
>         REG_S s1, PT_STATUS(sp)
>         REG_S s2, PT_EPC(sp)
>         REG_S s3, PT_BADADDR(sp)
>         REG_S s4, PT_CAUSE(sp)
>         REG_S s5, PT_TP(sp)
> +       REG_S s6, TASK_TI_ENVCFG(tp)
>
>         /*
>          * Set the scratch register to 0, so that if a recursive exception
> @@ -129,6 +131,10 @@ SYM_CODE_START_NOALIGN(ret_from_exception)
>         addi s0, sp, PT_SIZE_ON_STACK
>         REG_S s0, TASK_TI_KERNEL_SP(tp)
>
> +       /* restore envcfg bits for current thread */
> +       REG_L s0, TASK_TI_ENVCFG(tp)
> +       csrw CSR_ENVCFG, s0
> +
>         /* Save the kernel shadow call stack pointer */
>         scs_save_current
>
> --
> 2.43.0
>