[PATCH v10 1/6] arm64: ptrace: add NT_ARM_SYSTEM_CALL regset

From: AKASHI Takahiro
Date: Fri Nov 28 2014 - 00:27:21 EST


This regeset is intended to be used to get and set a system call number
while tracing.
There was some discussion about possible approaches to do so:

(1) modify x8 register with ptrace(PTRACE_SETREGSET) indirectly,
and update regs->syscallno later on in syscall_trace_enter(), or
(2) define a dedicated regset for this purpose as on s390, or
(3) support ptrace(PTRACE_SET_SYSCALL) as on arch/arm

Thinking of the fact that user_pt_regs doesn't expose 'syscallno' to
tracer as well as that secure_computing() expects a changed syscall number,
especially case of -1, to be visible before this function returns in
syscall_trace_enter(), (1) doesn't work well.
We will take (2) since it looks much cleaner.

Signed-off-by: AKASHI Takahiro <takahiro.akashi@xxxxxxxxxx>
---
arch/arm64/kernel/ptrace.c | 35 +++++++++++++++++++++++++++++++++++
include/uapi/linux/elf.h | 1 +
2 files changed, 36 insertions(+)

diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
index 8a4ae8e..f576781 100644
--- a/arch/arm64/kernel/ptrace.c
+++ b/arch/arm64/kernel/ptrace.c
@@ -551,6 +551,32 @@ static int tls_set(struct task_struct *target, const struct user_regset *regset,
return ret;
}

+static int system_call_get(struct task_struct *target,
+ const struct user_regset *regset,
+ unsigned int pos, unsigned int count,
+ void *kbuf, void __user *ubuf)
+{
+ int syscallno = task_pt_regs(target)->syscallno;
+
+ return user_regset_copyout(&pos, &count, &kbuf, &ubuf,
+ &syscallno, 0, -1);
+}
+
+static int system_call_set(struct task_struct *target,
+ const struct user_regset *regset,
+ unsigned int pos, unsigned int count,
+ const void *kbuf, const void __user *ubuf)
+{
+ int syscallno, ret;
+
+ ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf, &syscallno, 0, -1);
+ if (ret)
+ return ret;
+
+ task_pt_regs(target)->syscallno = syscallno;
+ return ret;
+}
+
enum aarch64_regset {
REGSET_GPR,
REGSET_FPR,
@@ -559,6 +585,7 @@ enum aarch64_regset {
REGSET_HW_BREAK,
REGSET_HW_WATCH,
#endif
+ REGSET_SYSTEM_CALL,
};

static const struct user_regset aarch64_regsets[] = {
@@ -608,6 +635,14 @@ static const struct user_regset aarch64_regsets[] = {
.set = hw_break_set,
},
#endif
+ [REGSET_SYSTEM_CALL] = {
+ .core_note_type = NT_ARM_SYSTEM_CALL,
+ .n = 1,
+ .size = sizeof(int),
+ .align = sizeof(int),
+ .get = system_call_get,
+ .set = system_call_set,
+ },
};

static const struct user_regset_view user_aarch64_view = {
diff --git a/include/uapi/linux/elf.h b/include/uapi/linux/elf.h
index ea9bf25..71e1d0e 100644
--- a/include/uapi/linux/elf.h
+++ b/include/uapi/linux/elf.h
@@ -397,6 +397,7 @@ typedef struct elf64_shdr {
#define NT_ARM_TLS 0x401 /* ARM TLS register */
#define NT_ARM_HW_BREAK 0x402 /* ARM hardware breakpoint registers */
#define NT_ARM_HW_WATCH 0x403 /* ARM hardware watchpoint registers */
+#define NT_ARM_SYSTEM_CALL 0x404 /* ARM system call number */
#define NT_METAG_CBUF 0x500 /* Metag catch buffer registers */
#define NT_METAG_RPIPE 0x501 /* Metag read pipeline state */
#define NT_METAG_TLS 0x502 /* Metag TLS pointer */
--
1.7.9.5

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