Re: [PATCH v2 1/2] riscv/ptrace: add new regset to access original a0 register

Hi Celeste,

On 03/12/2024 10:30, Celeste Liu wrote:

The orig_a0 is missing in struct user_regs_struct of riscv, and there is no way to add it without breaking UAPI. (See Link tag below)

Like NT_ARM_SYSTEM_CALL do, we add a new regset name NT_RISCV_ORIG_A0 to access original a0 register from userspace via ptrace API.

Link: https://lore.kernel.org/all/59505464-c84a-403d-972f-d4b2055eeaac@gmail.com/ Cc: stable@vger.kernel.org Signed-off-by: Celeste Liu uwu@coelacanthus.name

---

arch/riscv/kernel/ptrace.c | 32 ++++++++++++++++++++++++++++++++ include/uapi/linux/elf.h | 1 + 2 files changed, 33 insertions(+)

diff --git a/arch/riscv/kernel/ptrace.c b/arch/riscv/kernel/ptrace.c index ea67e9fb7a583683b922fe2c017ea61f3bc848db..18ce07ffb27bb1180667769eed800f6fdf96c083 100644 --- a/arch/riscv/kernel/ptrace.c +++ b/arch/riscv/kernel/ptrace.c @@ -31,6 +31,7 @@ enum riscv_regset { #ifdef CONFIG_RISCV_ISA_SUPM REGSET_TAGGED_ADDR_CTRL, #endif

• REGSET_ORIG_A0, };

static int riscv_gpr_get(struct task_struct *target, @@ -184,6 +185,29 @@ static int tagged_addr_ctrl_set(struct task_struct *target, } #endif +static int riscv_orig_a0_get(struct task_struct *target,

• 	     const struct user_regset *regset,
  

• 	     struct membuf to)
  

+{

• return membuf_store(&to, task_pt_regs(target)->orig_a0);

+}

+static int riscv_orig_a0_set(struct task_struct *target,

• 	     const struct user_regset *regset,
  

• 	     unsigned int pos, unsigned int count,
  

• 	     const void *kbuf, const void __user *ubuf)
  

+{

• unsigned long orig_a0 = task_pt_regs(target)->orig_a0;
• int ret;
• ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf, &orig_a0, 0, -1);
• if (ret)

• return ret;
  

• task_pt_regs(target)->orig_a0 = orig_a0;
• return ret;

+}

• static const struct user_regset riscv_user_regset[] = { [REGSET_X] = { .core_note_type = NT_PRSTATUS,

@@ -224,6 +248,14 @@ static const struct user_regset riscv_user_regset[] = { .set = tagged_addr_ctrl_set, }, #endif

• [REGSET_ORIG_A0] = {

• .core_note_type = NT_RISCV_ORIG_A0,
  

• .n = 1,
  

• .size = sizeof(elf_greg_t),
  

• .align = sizeof(elf_greg_t),
  

• .regset_get = riscv_orig_a0_get,
  

• .set = riscv_orig_a0_set,
  

• }, };

static const struct user_regset_view riscv_user_native_view = { diff --git a/include/uapi/linux/elf.h b/include/uapi/linux/elf.h index b44069d29cecc0f9de90ee66bfffd2137f4275a8..390060229601631da2fb27030d9fa2142e676c14 100644 --- a/include/uapi/linux/elf.h +++ b/include/uapi/linux/elf.h @@ -452,6 +452,7 @@ typedef struct elf64_shdr { #define NT_RISCV_CSR 0x900 /* RISC-V Control and Status Registers */ #define NT_RISCV_VECTOR 0x901 /* RISC-V vector registers */ #define NT_RISCV_TAGGED_ADDR_CTRL 0x902 /* RISC-V tagged address control (prctl()) */ +#define NT_RISCV_ORIG_A0 0x903 /* RISC-V original a0 register */ #define NT_LOONGARCH_CPUCFG 0xa00 /* LoongArch CPU config registers */ #define NT_LOONGARCH_CSR 0xa01 /* LoongArch control and status registers */ #define NT_LOONGARCH_LSX 0xa02 /* LoongArch Loongson SIMD Extension registers */

Do you know how far this should be backported? Does the following fixes tag make sense?

Fixes: e2c0cdfba7f6 ("RISC-V: User-facing API")

Thanks,

Alex