On Wed, Jan 27, 2021 at 02:53:07PM +0000, Dave Martin wrote:

On Tue, Jan 19, 2021 at 02:06:36PM -0800, Andrei Vagin wrote:

quoted

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 <redacted>

This approach looks like it works, though I still think adding an option
for this under PTRACE_SETOPTIONS would be less intrusive.

Dave, thank you for the feedback. I will prepare a patch with an option
and then we will see what looks better.

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...

quoted

---
 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.

I agree that REGSET_GPR_RAW looks better in this case.

quoted

 	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,

...

quoted

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?

shame on me :)

[...]

Cheers
---Dave

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