This commit updates the behavior of signal handling under !MMU
environment. 1) the stack preparation for the signal handlers and
2) restoration of stack after rt_sigreturn(2) syscall. Those are needed
as the stack usage on vfork(2) syscall is different.
It also adds the follow up routine for SIGSEGV as a signal delivery runs
in the same stack frame while we have to avoid endless SIGSEGV.
Signed-off-by: Hajime Tazaki <thehaj...@gmail.com>
---
arch/um/include/shared/kern_util.h | 3 +++
arch/um/kernel/trap.c | 10 ++++++++
arch/um/os-Linux/signal.c | 18 ++++++++++++++-
arch/x86/um/signal.c | 37 +++++++++++++++++++++++++++++-
4 files changed, 66 insertions(+), 2 deletions(-)
diff --git a/arch/um/include/shared/kern_util.h
b/arch/um/include/shared/kern_util.h
index f21dc8517538..bcc8d28279ae 100644
--- a/arch/um/include/shared/kern_util.h
+++ b/arch/um/include/shared/kern_util.h
@@ -62,6 +62,9 @@ extern int singlestepping(void);
extern void segv_handler(int sig, struct siginfo *unused_si, struct
uml_pt_regs *regs);
extern void winch(int sig, struct siginfo *unused_si, struct uml_pt_regs
*regs);
extern void fatal_sigsegv(void) __attribute__ ((noreturn));
+#ifndef CONFIG_MMU
+extern void sigsegv_post_routine(void);
+#endif
void um_idle_sleep(void);
diff --git a/arch/um/kernel/trap.c b/arch/um/kernel/trap.c
index a7519b3de4bf..b9b54e777894 100644
--- a/arch/um/kernel/trap.c
+++ b/arch/um/kernel/trap.c
@@ -174,6 +174,16 @@ void fatal_sigsegv(void)
os_dump_core();
}
+#ifndef CONFIG_MMU
+void sigsegv_post_routine(void)
+{
+ change_sig(SIGIO, 1);
+ change_sig(SIGALRM, 1);
+ change_sig(SIGWINCH, 1);
+ userspace(¤t->thread.regs.regs);
+}
+#endif
+
/**
* segv_handler() - the SIGSEGV handler
* @sig: the signal number
diff --git a/arch/um/os-Linux/signal.c b/arch/um/os-Linux/signal.c
index 52852018a3ad..a06622415d8f 100644
--- a/arch/um/os-Linux/signal.c
+++ b/arch/um/os-Linux/signal.c
@@ -36,7 +36,15 @@ static void sig_handler_common(int sig, struct siginfo *si,
mcontext_t *mc)
struct uml_pt_regs r;
int save_errno = errno;
- r.is_user = 0;
+#ifndef CONFIG_MMU
+ memset(&r, 0, sizeof(r));
+ /* mark is_user=1 when the IP is from userspace code. */
+ if (mc && (REGS_IP(mc->gregs) > uml_reserved
+ && REGS_IP(mc->gregs) < high_physmem))
+ r.is_user = 1;
+ else
+#endif
+ r.is_user = 0;
if (sig == SIGSEGV) {
/* For segfaults, we want the data from the sigcontext. */
get_regs_from_mc(&r, mc);
@@ -191,6 +199,7 @@ static void hard_handler(int sig, siginfo_t *si, void *p)
ucontext_t *uc = p;
mcontext_t *mc = &uc->uc_mcontext;
unsigned long pending = 1UL << sig;
+ int is_segv = 0;
do {
int nested, bail;
@@ -214,6 +223,7 @@ static void hard_handler(int sig, siginfo_t *si, void *p)
while ((sig = ffs(pending)) != 0){
sig--;
+ is_segv = (sig == SIGSEGV) ? 1 : 0;
pending &= ~(1 << sig);
(*handlers[sig])(sig, (struct siginfo *)si, mc);
}
@@ -227,6 +237,12 @@ static void hard_handler(int sig, siginfo_t *si, void *p)
if (!nested)
pending = from_irq_stack(nested);
} while (pending);
+
+#ifndef CONFIG_MMU
+ /* if there is SIGSEGV notified, let the userspace run w/ __noreturn */
+ if (is_segv)
+ sigsegv_post_routine();
+#endif
}
void set_handler(int sig)
diff --git a/arch/x86/um/signal.c b/arch/x86/um/signal.c
index 75087e85b6fd..b7365c75a967 100644
--- a/arch/x86/um/signal.c
+++ b/arch/x86/um/signal.c
@@ -371,6 +371,13 @@ int setup_signal_stack_si(unsigned long stack_top, struct
ksignal *ksig,
round_down(stack_top - sizeof(struct rt_sigframe), 16);
/* Add required space for math frame */
+#ifndef CONFIG_MMU
+ /*
+ * the sig_frame on !MMU needs be aligned for SSE as
+ * the frame is used as-is.
+ */
+ math_size = round_down(math_size, 16);
+#endif
frame = (struct rt_sigframe __user *)((unsigned long)frame - math_size);
/* Subtract 128 for a red zone and 8 for proper alignment */
@@ -417,6 +424,18 @@ int setup_signal_stack_si(unsigned long stack_top, struct
ksignal *ksig,
/* could use a vstub here */
return err;
+#ifndef CONFIG_MMU
+ /*
+ * we need to push handler address at top of stack, as
+ * __kernel_vsyscall, called after this returns with ret with
+ * stack contents, thus push the handler here.
+ */
+ frame = (struct rt_sigframe __user *) ((unsigned long) frame -
+ sizeof(unsigned long));
+ err |= __put_user((unsigned long)ksig->ka.sa.sa_handler,
+ (unsigned long *)frame);
+#endif
+
if (err)
return err;
@@ -442,9 +461,25 @@ SYSCALL_DEFINE0(rt_sigreturn)
unsigned long sp = PT_REGS_SP(¤t->thread.regs);
struct rt_sigframe __user *frame =
(struct rt_sigframe __user *)(sp - sizeof(long));
- struct ucontext __user *uc = &frame->uc;
+ struct ucontext __user *uc;
sigset_t set;
+#ifndef CONFIG_MMU
+ /**
+ * we enter here with:
+ *
+ * __restore_rt:
+ * mov $15, %rax
+ * call *%rax (translated from syscall)
+ *
+ * (code is from musl libc)
+ * so, stack needs to be popped of "call"ed address before
+ * looking at rt_sigframe.
+ */
+ frame = (struct rt_sigframe __user *)((unsigned long)frame +
sizeof(long));
+#endif
+ uc = &frame->uc;
+
if (copy_from_user(&set, &uc->uc_sigmask, sizeof(set)))
goto segfault;
--
2.43.0
