ip/r12 for AArch32 and x7 for AArch64 is used to indicate whether or not the stop has been signalled from syscall entry or syscall exit. This means that:
- Any writes by the tracer to this register during the stop are ignored/discarded. - The actual value of the register is not available during the stop, so the tracer cannot save it and restore it later. Right now, these registers are clobbered in tracehook_report_syscall. This change moves this logic to gpr_get and compat_gpr_get where registers are copied into a user-space buffer. This will allow to change these registers and to introduce a new NT_ARM_PRSTATUS command to get the full set of registers. Signed-off-by: Andrei Vagin <[email protected]> --- arch/arm64/include/asm/ptrace.h | 5 ++ arch/arm64/kernel/ptrace.c | 104 +++++++++++++++++++------------- 2 files changed, 67 insertions(+), 42 deletions(-) diff --git a/arch/arm64/include/asm/ptrace.h b/arch/arm64/include/asm/ptrace.h index e58bca832dff..0a9552b4f61e 100644 --- a/arch/arm64/include/asm/ptrace.h +++ b/arch/arm64/include/asm/ptrace.h @@ -170,6 +170,11 @@ static inline unsigned long pstate_to_compat_psr(const unsigned long pstate) return psr; } +enum ptrace_syscall_dir { + PTRACE_SYSCALL_ENTER = 0, + PTRACE_SYSCALL_EXIT, +}; + /* * This struct defines the way the registers are stored on the stack during an * exception. Note that sizeof(struct pt_regs) has to be a multiple of 16 (for diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c index 8ac487c84e37..1863f080cb07 100644 --- a/arch/arm64/kernel/ptrace.c +++ b/arch/arm64/kernel/ptrace.c @@ -40,6 +40,7 @@ #include <asm/syscall.h> #include <asm/traps.h> #include <asm/system_misc.h> +#include <asm/ptrace.h> #define CREATE_TRACE_POINTS #include <trace/events/syscalls.h> @@ -561,7 +562,33 @@ static int gpr_get(struct task_struct *target, struct membuf to) { struct user_pt_regs *uregs = &task_pt_regs(target)->user_regs; - return membuf_write(&to, uregs, sizeof(*uregs)); + unsigned long saved_reg; + int ret; + + /* + * We have some ABI weirdness here in the way that we handle syscall + * exit stops because we indicate whether or not the stop has been + * signalled from syscall entry or syscall exit by clobbering the general + * purpose register x7. + */ + switch (target->ptrace_message) { + case PTRACE_EVENTMSG_SYSCALL_ENTRY: + saved_reg = uregs->regs[7]; + uregs->regs[7] = PTRACE_SYSCALL_ENTER; + break; + case PTRACE_EVENTMSG_SYSCALL_EXIT: + saved_reg = uregs->regs[7]; + uregs->regs[7] = PTRACE_SYSCALL_EXIT; + break; + } + + ret = membuf_write(&to, uregs, sizeof(*uregs)); + + if (target->ptrace_message == PTRACE_EVENTMSG_SYSCALL_ENTRY || + target->ptrace_message == PTRACE_EVENTMSG_SYSCALL_EXIT) + uregs->regs[7] = saved_reg; + + return ret; } static int gpr_set(struct task_struct *target, const struct user_regset *regset, @@ -1221,10 +1248,40 @@ static int compat_gpr_get(struct task_struct *target, const struct user_regset *regset, struct membuf to) { + compat_ulong_t r12; + bool overwrite_r12; int i = 0; - while (to.left) - membuf_store(&to, compat_get_user_reg(target, i++)); + /* + * We have some ABI weirdness here in the way that we handle syscall + * exit stops because we indicate whether or not the stop has been + * signalled from syscall entry or syscall exit by clobbering the + * general purpose register r12. + */ + switch (target->ptrace_message) { + case PTRACE_EVENTMSG_SYSCALL_ENTRY: + r12 = PTRACE_SYSCALL_ENTER; + overwrite_r12 = true; + break; + case PTRACE_EVENTMSG_SYSCALL_EXIT: + r12 = PTRACE_SYSCALL_EXIT; + overwrite_r12 = true; + break; + default: + overwrite_r12 = false; + break; + } + + while (to.left) { + compat_ulong_t val; + + if (!overwrite_r12 || i != 12) + val = compat_get_user_reg(target, i++); + else + val = r12; + membuf_store(&to, val); + } + return 0; } @@ -1740,53 +1797,16 @@ long arch_ptrace(struct task_struct *child, long request, return ptrace_request(child, request, addr, data); } -enum ptrace_syscall_dir { - PTRACE_SYSCALL_ENTER = 0, - PTRACE_SYSCALL_EXIT, -}; - static void tracehook_report_syscall(struct pt_regs *regs, enum ptrace_syscall_dir dir) { - int regno; - unsigned long saved_reg; - - /* - * We have some ABI weirdness here in the way that we handle syscall - * exit stops because we indicate whether or not the stop has been - * signalled from syscall entry or syscall exit by clobbering a general - * purpose register (ip/r12 for AArch32, x7 for AArch64) in the tracee - * and restoring its old value after the stop. This means that: - * - * - Any writes by the tracer to this register during the stop are - * ignored/discarded. - * - * - The actual value of the register is not available during the stop, - * so the tracer cannot save it and restore it later. - * - * - Syscall stops behave differently to seccomp and pseudo-step traps - * (the latter do not nobble any registers). - */ - regno = (is_compat_task() ? 12 : 7); - saved_reg = regs->regs[regno]; - regs->regs[regno] = dir; - if (dir == PTRACE_SYSCALL_ENTER) { if (tracehook_report_syscall_entry(regs)) forget_syscall(regs); - regs->regs[regno] = saved_reg; - } else if (!test_thread_flag(TIF_SINGLESTEP)) { - tracehook_report_syscall_exit(regs, 0); - regs->regs[regno] = saved_reg; } else { - regs->regs[regno] = saved_reg; + int singlestep = test_thread_flag(TIF_SINGLESTEP); - /* - * Signal a pseudo-step exception since we are stepping but - * tracer modifications to the registers may have rewound the - * state machine. - */ - tracehook_report_syscall_exit(regs, 1); + tracehook_report_syscall_exit(regs, singlestep); } } -- 2.29.2
