On Tue, Jan 19, 2021 at 02:06:36PM -0800, Andrei Vagin wrote:
> This is an alternative to NT_PRSTATUS that clobbers ip/r12 on AArch32,
> x7 on AArch64 when a tracee is stopped in syscall entry or syscall exit
> traps.
>
> Signed-off-by: Andrei Vagin <[email protected]>
This approach looks like it works, though I still think adding an option
for this under PTRACE_SETOPTIONS would be less intrusive.
Adding a shadow regset like this also looks like it would cause the gp
regs to be pointlessly be dumped twice in a core dump. Avoiding that
might require hacks in the core code...
> ---
> arch/arm64/kernel/ptrace.c | 39 ++++++++++++++++++++++++++++++++++++++
> include/uapi/linux/elf.h | 1 +
> 2 files changed, 40 insertions(+)
>
> diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
> index 1863f080cb07..b8e4c2ddf636 100644
> --- a/arch/arm64/kernel/ptrace.c
> +++ b/arch/arm64/kernel/ptrace.c
> @@ -591,6 +591,15 @@ static int gpr_get(struct task_struct *target,
> return ret;
> }
>
> +static int gpr_get_full(struct task_struct *target,
> + const struct user_regset *regset,
> + struct membuf to)
> +{
> + struct user_pt_regs *uregs = &task_pt_regs(target)->user_regs;
> +
> + return membuf_write(&to, uregs, sizeof(*uregs));
> +}
> +
> static int gpr_set(struct task_struct *target, const struct user_regset
> *regset,
> unsigned int pos, unsigned int count,
> const void *kbuf, const void __user *ubuf)
> @@ -1088,6 +1097,7 @@ static int tagged_addr_ctrl_set(struct task_struct
> *target, const struct
>
> enum aarch64_regset {
> REGSET_GPR,
> + REGSET_GPR_FULL,
If we go with this approach, "REGSET_GPR_RAW" might be a preferable
name. Both regs represent all the regs ("full"), but REGSET_GPR is
mangled by the kernel.
> REGSET_FPR,
> REGSET_TLS,
> #ifdef CONFIG_HAVE_HW_BREAKPOINT
> @@ -1119,6 +1129,14 @@ static const struct user_regset aarch64_regsets[] = {
> .regset_get = gpr_get,
> .set = gpr_set
> },
> + [REGSET_GPR_FULL] = {
> + .core_note_type = NT_ARM_PRSTATUS,
Similarly, something like NT_ARM_PRSTATUS_RAW or similar.
> + .n = sizeof(struct user_pt_regs) / sizeof(u64),
> + .size = sizeof(u64),
> + .align = sizeof(u64),
> + .regset_get = gpr_get_full,
> + .set = gpr_set
> + },
> [REGSET_FPR] = {
> .core_note_type = NT_PRFPREG,
> .n = sizeof(struct user_fpsimd_state) / sizeof(u32),
> @@ -1225,6 +1243,7 @@ static const struct user_regset_view user_aarch64_view
> = {
> #ifdef CONFIG_COMPAT
> enum compat_regset {
> REGSET_COMPAT_GPR,
> + REGSET_COMPAT_GPR_FULL,
> REGSET_COMPAT_VFP,
> };
>
> @@ -1285,6 +1304,18 @@ static int compat_gpr_get(struct task_struct *target,
> return 0;
> }
>
> +/* compat_gpr_get_full doesn't overwrite x12 like compat_gpr_get. */
> +static int compat_gpr_get_full(struct task_struct *target,
> + const struct user_regset *regset,
> + struct membuf to)
> +{
> + int i = 0;
> +
> + while (to.left)
> + membuf_store(&to, compat_get_user_reg(target, i++));
> + return 0;
> +}
> +
> static int compat_gpr_set(struct task_struct *target,
> const struct user_regset *regset,
> unsigned int pos, unsigned int count,
> @@ -1435,6 +1466,14 @@ static const struct user_regset aarch32_regsets[] = {
> .regset_get = compat_gpr_get,
> .set = compat_gpr_set
> },
> + [REGSET_COMPAT_GPR_FULL] = {
> + .core_note_type = NT_ARM_PRSTATUS,
> + .n = COMPAT_ELF_NGREG,
> + .size = sizeof(compat_elf_greg_t),
> + .align = sizeof(compat_elf_greg_t),
> + .regset_get = compat_gpr_get_full,
> + .set = compat_gpr_set
> + },
> [REGSET_COMPAT_VFP] = {
> .core_note_type = NT_ARM_VFP,
> .n = VFP_STATE_SIZE / sizeof(compat_ulong_t),
> diff --git a/include/uapi/linux/elf.h b/include/uapi/linux/elf.h
> index 30f68b42eeb5..a2086d19263a 100644
> --- a/include/uapi/linux/elf.h
> +++ b/include/uapi/linux/elf.h
> @@ -426,6 +426,7 @@ typedef struct elf64_shdr {
> #define NT_ARM_PACA_KEYS 0x407 /* ARM pointer authentication address
> keys */
> #define NT_ARM_PACG_KEYS 0x408 /* ARM pointer authentication generic
> key */
> #define NT_ARM_TAGGED_ADDR_CTRL 0x409 /* arm64 tagged address control
> (prctl()) */
What happened to 0x40a..0x40f?
[...]
Cheers
---Dave
