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Mon, 01 Feb 2021 11:41:59 -0800 (PST) From: Andrei Vagin To: Will Deacon , Catalin Marinas Subject: [PATCH 1/3] arm64/ptrace: don't clobber task registers on syscall entry/exit traps Date: Mon, 1 Feb 2021 11:40:10 -0800 Message-Id: <20210201194012.524831-2-avagin@gmail.com> X-Mailer: git-send-email 2.29.2 In-Reply-To: <20210201194012.524831-1-avagin@gmail.com> References: <20210201194012.524831-1-avagin@gmail.com> MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210201_144204_182233_E080B928 X-CRM114-Status: GOOD ( 24.11 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Anthony Steinhauser , linux-api@vger.kernel.org, Oleg Nesterov , linux-kernel@vger.kernel.org, Keno Fischer , Andrei Vagin , Dave Martin , linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org 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 the 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 ptrace option to get the full set of registers. Signed-off-by: Andrei Vagin --- arch/arm64/include/asm/ptrace.h | 5 ++ arch/arm64/kernel/ptrace.c | 104 ++++++++++++++++++++------------ 2 files changed, 69 insertions(+), 40 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..39da03104528 100644 --- a/arch/arm64/kernel/ptrace.c +++ b/arch/arm64/kernel/ptrace.c @@ -40,6 +40,7 @@ #include #include #include +#include #define CREATE_TRACE_POINTS #include @@ -561,7 +562,31 @@ 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. + */ + saved_reg = uregs->regs[7]; + + switch (target->ptrace_message) { + case PTRACE_EVENTMSG_SYSCALL_ENTRY: + uregs->regs[7] = PTRACE_SYSCALL_ENTER; + break; + case PTRACE_EVENTMSG_SYSCALL_EXIT: + uregs->regs[7] = PTRACE_SYSCALL_EXIT; + break; + } + + ret = membuf_write(&to, uregs, sizeof(*uregs)); + + uregs->regs[7] = saved_reg; + + return ret; } static int gpr_set(struct task_struct *target, const struct user_regset *regset, @@ -575,6 +600,17 @@ static int gpr_set(struct task_struct *target, const struct user_regset *regset, if (ret) return ret; + /* + * Historically, x7 can't be changed if the stop has been signalled + * from syscall-enter of syscall-exit. + */ + switch (target->ptrace_message) { + case PTRACE_EVENTMSG_SYSCALL_ENTRY: + case PTRACE_EVENTMSG_SYSCALL_EXIT: + newregs.regs[7] = task_pt_regs(target)->regs[7]; + break; + } + if (!valid_user_regs(&newregs, target)) return -EINVAL; @@ -1206,6 +1242,20 @@ static inline compat_ulong_t compat_get_user_reg(struct task_struct *task, int i struct pt_regs *regs = task_pt_regs(task); switch (idx) { + case 12: + /* + * 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 (task->ptrace_message) { + case PTRACE_EVENTMSG_SYSCALL_ENTRY: + return PTRACE_SYSCALL_ENTER; + case PTRACE_EVENTMSG_SYSCALL_EXIT: + return PTRACE_SYSCALL_EXIT; + } + return regs->regs[idx]; case 15: return regs->pc; case 16: @@ -1282,6 +1332,17 @@ static int compat_gpr_set(struct task_struct *target, } + /* + * Historically, x12 can't be changed if the stop has been signalled + * from syscall-enter of syscall-exit. + */ + switch (target->ptrace_message) { + case PTRACE_EVENTMSG_SYSCALL_ENTRY: + case PTRACE_EVENTMSG_SYSCALL_EXIT: + newregs.regs[12] = task_pt_regs(target)->regs[12]; + break; + } + if (valid_user_regs(&newregs.user_regs, target)) *task_pt_regs(target) = newregs; else @@ -1740,53 +1801,16 @@ 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 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel