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Message-Id: <20180514094640.27569-10-mark.rutland@arm.com>
Date: Mon, 14 May 2018 10:46:31 +0100
From: Mark Rutland <mark.rutland@....com>
To: linux-arm-kernel@...ts.infradead.org
Cc: linux-kernel@...r.kernel.org, catalin.marinas@....com,
dave.martin@....com, james.morse@....com,
linux@...inikbrodowski.net, linux-fsdevel@...r.kernel.org,
marc.zyngier@....com, mark.rutland@....com,
viro@...iv.linux.org.uk, will.deacon@....com
Subject: [PATCH 09/18] arm64: convert syscall trace logic to C
Currently syscall tracing is a tricky assembly state machine, which can
be rather difficult to follow, and even harder to modify. Before we
start fiddling with it for pt_regs syscalls, let's convert it to C.
This is not intended to have any functional change.
Signed-off-by: Mark Rutland <mark.rutland@....com>
Cc: Catalin Marinas <catalin.marinas@....com>
Cc: Will Deacon <will.deacon@....com>
---
arch/arm64/kernel/entry.S | 53 ++----------------------------------------
arch/arm64/kernel/syscall.c | 56 +++++++++++++++++++++++++++++++++++++++++++--
2 files changed, 56 insertions(+), 53 deletions(-)
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index d6e057500eaf..5c60369b52fc 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -866,24 +866,6 @@ el0_error_naked:
b ret_to_user
ENDPROC(el0_error)
-
-/*
- * This is the fast syscall return path. We do as little as possible here,
- * and this includes saving x0 back into the kernel stack.
- */
-ret_fast_syscall:
- disable_daif
- ldr x1, [tsk, #TSK_TI_FLAGS] // re-check for syscall tracing
- and x2, x1, #_TIF_SYSCALL_WORK
- cbnz x2, ret_fast_syscall_trace
- and x2, x1, #_TIF_WORK_MASK
- cbnz x2, work_pending
- enable_step_tsk x1, x2
- kernel_exit 0
-ret_fast_syscall_trace:
- enable_daif
- b __sys_trace_return_skipped // we already saved x0
-
/*
* Ok, we need to do extra processing, enter the slow path.
*/
@@ -939,44 +921,13 @@ alternative_else_nop_endif
#endif
el0_svc_naked: // compat entry point
- stp x0, xscno, [sp, #S_ORIG_X0] // save the original x0 and syscall number
- enable_daif
- ct_user_exit 1
-
- tst x16, #_TIF_SYSCALL_WORK // check for syscall hooks
- b.ne __sys_trace
mov x0, sp
mov w1, wscno
mov w2, wsc_nr
mov x3, stbl
- bl invoke_syscall
- b ret_fast_syscall
-ENDPROC(el0_svc)
-
- /*
- * This is the really slow path. We're going to be doing context
- * switches, and waiting for our parent to respond.
- */
-__sys_trace:
- 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, #NO_SYSCALL // skip the syscall?
- b.eq __sys_trace_return_skipped
-
- mov x0, sp
- mov w1, wscno
- mov w2, wsc_nr
- mov x3, stbl
- bl invoke_syscall
-
-__sys_trace_return_skipped:
- mov x0, sp
- bl syscall_trace_exit
+ bl el0_svc_common
b ret_to_user
+ENDPROC(el0_svc)
.popsection // .entry.text
diff --git a/arch/arm64/kernel/syscall.c b/arch/arm64/kernel/syscall.c
index 58d7569f47df..5df857e32b48 100644
--- a/arch/arm64/kernel/syscall.c
+++ b/arch/arm64/kernel/syscall.c
@@ -1,8 +1,13 @@
// SPDX-License-Identifier: GPL-2.0
+#include <linux/compiler.h>
+#include <linux/context_tracking.h>
#include <linux/nospec.h>
#include <linux/ptrace.h>
+#include <asm/daifflags.h>
+#include <asm/thread_info.h>
+
long do_ni_syscall(struct pt_regs *regs);
typedef long (*syscall_fn_t)(unsigned long, unsigned long,
@@ -16,8 +21,8 @@ static void __invoke_syscall(struct pt_regs *regs, syscall_fn_t syscall_fn)
regs->regs[4], regs->regs[5]);
}
-asmlinkage void invoke_syscall(struct pt_regs *regs, int scno, int sc_nr,
- syscall_fn_t syscall_table[])
+static void invoke_syscall(struct pt_regs *regs, int scno, int sc_nr,
+ syscall_fn_t syscall_table[])
{
if (scno < sc_nr) {
syscall_fn_t syscall_fn;
@@ -27,3 +32,50 @@ asmlinkage void invoke_syscall(struct pt_regs *regs, int scno, int sc_nr,
regs->regs[0] = do_ni_syscall(regs);
}
}
+
+static inline bool has_syscall_work(unsigned long flags)
+{
+ return unlikely(flags & _TIF_SYSCALL_WORK);
+}
+
+int syscall_trace_enter(struct pt_regs *regs);
+void syscall_trace_exit(struct pt_regs *regs);
+
+asmlinkage void el0_svc_common(struct pt_regs *regs, int scno, int sc_nr,
+ syscall_fn_t syscall_table[])
+{
+ unsigned long flags = current_thread_info()->flags;
+
+ regs->orig_x0 = regs->regs[0];
+ regs->syscallno = scno;
+
+ local_daif_restore(DAIF_PROCCTX);
+ user_exit();
+
+ if (has_syscall_work(flags)) {
+ /* set default errno for user-issued syscall(-1) */
+ if (scno == NO_SYSCALL)
+ regs->regs[0] = -ENOSYS;
+ scno = syscall_trace_enter(regs);
+ if (scno == NO_SYSCALL)
+ goto trace_exit;
+ }
+
+ invoke_syscall(regs, scno, sc_nr, syscall_table);
+
+ /*
+ * The tracing status may have changed under our feet, so we have to
+ * check again. However, if we were tracing entry, then we always trace
+ * exit regardless, as the old entry assembly did.
+ */
+ if (!has_syscall_work(flags)) {
+ local_daif_mask();
+ flags = current_thread_info()->flags;
+ if (!has_syscall_work(flags))
+ return;
+ local_daif_restore(DAIF_PROCCTX);
+ }
+
+trace_exit:
+ syscall_trace_exit(regs);
+}
--
2.11.0
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