[PATCH 2/2] arm64: Abstract syscallno manipulation
Dave Martin
Dave.Martin at arm.com
Tue Jul 18 05:41:44 PDT 2017
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 <Dave.Martin at arm.com>
---
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 | 8 ++++----
arch/arm64/kernel/signal32.c | 2 +-
6 files changed, 32 insertions(+), 13 deletions(-)
diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h
index 379def1..b7334f1 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 21c87dc..3a2d6cc 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 <linux/bug.h>
+#include <linux/types.h>
/* 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(int syscallno)
+{
+ return 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 3bf0bd7..cace76d 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 de77480..28619b5 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 4d04b89..3a59dae 100644
--- a/arch/arm64/kernel/signal.c
+++ b/arch/arm64/kernel/signal.c
@@ -387,7 +387,7 @@ 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)
@@ -679,7 +679,7 @@ static void do_signal(struct pt_regs *regs)
/*
* If we were from a system call, check for system call restarting...
*/
- if (syscall >= 0) {
+ if (in_syscall(syscall)) {
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(syscall) && 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 d98ca76..4e5a664 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);
--
2.1.4
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