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arm64: ptrace: add NT_ARM_SYSTEM_CALL regset

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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@linaro.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
This commit is contained in:
AKASHI Takahiro 2014-11-28 05:26:34 +00:00 committed by Will Deacon
parent 034edabe6c
commit 766a85d7bc
2 changed files with 36 additions and 0 deletions
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35
arch/arm64/kernel/ptrace.c
View file

@ -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 = {

1
include/uapi/linux/elf.h
View file

@ -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 */