Re: [PATCH v4 06/10] riscv: Allow ptrace control of the tagged address ABI

[Charlie Jenkins <charlie@rivosinc.com>]

On Wed, Oct 16, 2024 at 12:50:32PM -0500, Samuel Holland wrote:
> Hi Charlie,
> 
> On 2024-09-12 9:51 PM, Charlie Jenkins wrote:
> > On Wed, Aug 28, 2024 at 06:01:28PM -0700, Samuel Holland wrote:
> >> This allows a tracer to control the ABI of the tracee, as on arm64.
> >>
> >> Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
> >> ---
> > 
> > Since this code is identical to the arm64 port, could it be extracted
> > out into the generic ptrace.c and ifdef on either CONFIG_RISCV_ISA_SUPM
> > or CONFIG_ARM64_TAGGED_ADDR_ABI by adding some generic flag like
> > CONFIG_HAVE_ARCH_TAGGED_ADDR_ABI?
> 
> Yes, it could be factored out, though I don't know if it is worth the overhead
> for these two trivial functions. I don't see any other code like this outside of
> arch/.

In my ideal world there is just a generic header somewhere so the only
"overhead" is creating the generic header. But I will defer to you on
whether it is worthwhile.

- Charlie

> 
> Regards,
> Samuel
> 
> >>
> >> (no changes since v1)
> >>
> >>  arch/riscv/kernel/ptrace.c | 42 ++++++++++++++++++++++++++++++++++++++
> >>  include/uapi/linux/elf.h   |  1 +
> >>  2 files changed, 43 insertions(+)
> >>
> >> diff --git a/arch/riscv/kernel/ptrace.c b/arch/riscv/kernel/ptrace.c
> >> index 92731ff8c79a..ea67e9fb7a58 100644
> >> --- a/arch/riscv/kernel/ptrace.c
> >> +++ b/arch/riscv/kernel/ptrace.c
> >> @@ -28,6 +28,9 @@ enum riscv_regset {
> >>  #ifdef CONFIG_RISCV_ISA_V
> >>  	REGSET_V,
> >>  #endif
> >> +#ifdef CONFIG_RISCV_ISA_SUPM
> >> +	REGSET_TAGGED_ADDR_CTRL,
> >> +#endif
> >>  };
> >>  
> >>  static int riscv_gpr_get(struct task_struct *target,
> >> @@ -152,6 +155,35 @@ static int riscv_vr_set(struct task_struct *target,
> >>  }
> >>  #endif
> >>  
> >> +#ifdef CONFIG_RISCV_ISA_SUPM
> >> +static int tagged_addr_ctrl_get(struct task_struct *target,
> >> +				const struct user_regset *regset,
> >> +				struct membuf to)
> >> +{
> >> +	long ctrl = get_tagged_addr_ctrl(target);
> >> +
> >> +	if (IS_ERR_VALUE(ctrl))
> >> +		return ctrl;
> >> +
> >> +	return membuf_write(&to, &ctrl, sizeof(ctrl));
> >> +}
> >> +
> >> +static int tagged_addr_ctrl_set(struct task_struct *target,
> >> +				const struct user_regset *regset,
> >> +				unsigned int pos, unsigned int count,
> >> +				const void *kbuf, const void __user *ubuf)
> >> +{
> >> +	int ret;
> >> +	long ctrl;
> >> +
> >> +	ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf, &ctrl, 0, -1);
> >> +	if (ret)
> >> +		return ret;
> >> +
> >> +	return set_tagged_addr_ctrl(target, ctrl);
> >> +}
> >> +#endif
> >> +
> >>  static const struct user_regset riscv_user_regset[] = {
> >>  	[REGSET_X] = {
> >>  		.core_note_type = NT_PRSTATUS,
> >> @@ -182,6 +214,16 @@ static const struct user_regset riscv_user_regset[] = {
> >>  		.set = riscv_vr_set,
> >>  	},
> >>  #endif
> >> +#ifdef CONFIG_RISCV_ISA_SUPM
> >> +	[REGSET_TAGGED_ADDR_CTRL] = {
> >> +		.core_note_type = NT_RISCV_TAGGED_ADDR_CTRL,
> >> +		.n = 1,
> >> +		.size = sizeof(long),
> >> +		.align = sizeof(long),
> >> +		.regset_get = tagged_addr_ctrl_get,
> >> +		.set = tagged_addr_ctrl_set,
> >> +	},
> >> +#endif
> >>  };
> >>  
> >>  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 b54b313bcf07..9a32532d7264 100644
> >> --- a/include/uapi/linux/elf.h
> >> +++ b/include/uapi/linux/elf.h
> >> @@ -448,6 +448,7 @@ typedef struct elf64_shdr {
> >>  #define NT_MIPS_MSA	0x802		/* MIPS SIMD registers */
> >>  #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_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 */
> >> -- 
> >> 2.45.1
> >>
> >>
> >> _______________________________________________
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>