From 17c28958600928109049a3bcc814b0d5bfb1ff3a Mon Sep 17 00:00:00 2001 From: Dave Martin Date: Tue, 1 Aug 2017 15:35:54 +0100 Subject: [PATCH] arm64: Abstract syscallno manipulation The -1 "no syscall" value is written in various ways, shared with the user ABI in some places, and generally obscure. This patch attempts to make things a little more consistent and readable by replacing all these uses with a single #define. A couple of symbolic helpers are provided to clarify the intent further. Because the in-syscall check in do_signal() is changed from >= 0 to != NO_SYSCALL by this patch, different behaviour may be observable if syscallno is set to values less than -1 by a tracer. However, this is not different from the behaviour that is already observable if a tracer sets syscallno to a value >= __NR_(compat_)syscalls. It appears that this can cause spurious syscall restarting, but that is not a new behaviour either, and does not appear harmful. Signed-off-by: Dave Martin Acked-by: Will Deacon Signed-off-by: Catalin Marinas --- arch/arm64/include/asm/processor.h | 2 +- arch/arm64/include/asm/ptrace.h | 21 +++++++++++++++++++++ arch/arm64/kernel/entry.S | 10 ++++------ arch/arm64/kernel/ptrace.c | 2 +- arch/arm64/kernel/signal.c | 10 +++++----- arch/arm64/kernel/signal32.c | 2 +- 6 files changed, 33 insertions(+), 14 deletions(-) diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h index 379def1d6b67..b7334f11c4cf 100644 --- a/arch/arm64/include/asm/processor.h +++ b/arch/arm64/include/asm/processor.h @@ -112,7 +112,7 @@ void tls_preserve_current_state(void); static inline void start_thread_common(struct pt_regs *regs, unsigned long pc) { memset(regs, 0, sizeof(*regs)); - regs->syscallno = ~0; + forget_syscall(regs); regs->pc = pc; } diff --git a/arch/arm64/include/asm/ptrace.h b/arch/arm64/include/asm/ptrace.h index 21c87dc240e1..4f64373b84fd 100644 --- a/arch/arm64/include/asm/ptrace.h +++ b/arch/arm64/include/asm/ptrace.h @@ -72,8 +72,19 @@ #define COMPAT_PT_TEXT_ADDR 0x10000 #define COMPAT_PT_DATA_ADDR 0x10004 #define COMPAT_PT_TEXT_END_ADDR 0x10008 + +/* + * If pt_regs.syscallno == NO_SYSCALL, then the thread is not executing + * a syscall -- i.e., its most recent entry into the kernel from + * userspace was not via SVC, or otherwise a tracer cancelled the syscall. + * + * This must have the value -1, for ABI compatibility with ptrace etc. + */ +#define NO_SYSCALL (-1) + #ifndef __ASSEMBLY__ #include +#include /* sizeof(struct user) for AArch32 */ #define COMPAT_USER_SZ 296 @@ -128,6 +139,16 @@ struct pt_regs { u64 unused; // maintain 16 byte alignment }; +static inline bool in_syscall(struct pt_regs const *regs) +{ + return regs->syscallno != NO_SYSCALL; +} + +static inline void forget_syscall(struct pt_regs *regs) +{ + regs->syscallno = NO_SYSCALL; +} + #define MAX_REG_OFFSET offsetof(struct pt_regs, pstate) #define arch_has_single_step() (1) diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S index 3bf0bd7a2f29..cace76d17535 100644 --- a/arch/arm64/kernel/entry.S +++ b/arch/arm64/kernel/entry.S @@ -138,11 +138,9 @@ alternative_else_nop_endif stp x22, x23, [sp, #S_PC] - /* - * Set syscallno to -1 by default (overridden later if real syscall). - */ + /* Not in a syscall by default (el0_svc overwrites for real syscall) */ .if \el == 0 - mvn w21, wzr + mov w21, #NO_SYSCALL str w21, [sp, #S_SYSCALLNO] .endif @@ -825,13 +823,13 @@ ENDPROC(el0_svc) * switches, and waiting for our parent to respond. */ __sys_trace: - cmp wscno, #-1 // user-issued syscall(-1)? + cmp wscno, #NO_SYSCALL // user-issued syscall(-1)? b.ne 1f mov x0, #-ENOSYS // set default errno if so str x0, [sp, #S_X0] 1: mov x0, sp bl syscall_trace_enter - cmp w0, #-1 // skip the syscall? + cmp w0, #NO_SYSCALL // skip the syscall? b.eq __sys_trace_return_skipped mov wscno, w0 // syscall number (possibly new) mov x1, sp // pointer to regs diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c index de774805f672..28619b5b6746 100644 --- a/arch/arm64/kernel/ptrace.c +++ b/arch/arm64/kernel/ptrace.c @@ -1363,7 +1363,7 @@ static void tracehook_report_syscall(struct pt_regs *regs, if (dir == PTRACE_SYSCALL_EXIT) tracehook_report_syscall_exit(regs, 0); else if (tracehook_report_syscall_entry(regs)) - regs->syscallno = ~0; + forget_syscall(regs); regs->regs[regno] = saved_reg; } diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c index 4d04b891c00d..4991e87f80cc 100644 --- a/arch/arm64/kernel/signal.c +++ b/arch/arm64/kernel/signal.c @@ -36,6 +36,7 @@ #include #include #include +#include #include #include @@ -387,7 +388,7 @@ static int restore_sigframe(struct pt_regs *regs, /* * Avoid sys_rt_sigreturn() restarting. */ - regs->syscallno = ~0; + forget_syscall(regs); err |= !valid_user_regs(®s->user_regs, current); if (err == 0) @@ -673,13 +674,12 @@ static void do_signal(struct pt_regs *regs) { unsigned long continue_addr = 0, restart_addr = 0; int retval = 0; - int syscall = regs->syscallno; struct ksignal ksig; /* * If we were from a system call, check for system call restarting... */ - if (syscall >= 0) { + if (in_syscall(regs)) { continue_addr = regs->pc; restart_addr = continue_addr - (compat_thumb_mode(regs) ? 2 : 4); retval = regs->regs[0]; @@ -687,7 +687,7 @@ static void do_signal(struct pt_regs *regs) /* * Avoid additional syscall restarting via ret_to_user. */ - regs->syscallno = ~0; + forget_syscall(regs); /* * Prepare for system call restart. We do this here so that a @@ -731,7 +731,7 @@ static void do_signal(struct pt_regs *regs) * Handle restarting a different system call. As above, if a debugger * has chosen to restart at a different PC, ignore the restart. */ - if (syscall >= 0 && regs->pc == restart_addr) { + if (in_syscall(regs) && regs->pc == restart_addr) { if (retval == -ERESTART_RESTARTBLOCK) setup_restart_syscall(regs); user_rewind_single_step(current); diff --git a/arch/arm64/kernel/signal32.c b/arch/arm64/kernel/signal32.c index d98ca76cbd39..4e5a664be04b 100644 --- a/arch/arm64/kernel/signal32.c +++ b/arch/arm64/kernel/signal32.c @@ -354,7 +354,7 @@ static int compat_restore_sigframe(struct pt_regs *regs, /* * Avoid compat_sys_sigreturn() restarting. */ - regs->syscallno = ~0; + forget_syscall(regs); err |= !valid_user_regs(®s->user_regs, current); -- 2.20.1