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/os-Linux/signal.c | 16 +++++++++++++++-
arch/x86/um/signal.c | 37 ++++++++++++++++++++++++++++++++++++-
2 files changed, 51 insertions(+), 2 deletions(-)
diff --git a/arch/um/os-Linux/signal.c b/arch/um/os-Linux/signal.c
index c0d1fb1fc0c4..de3ed8fc0268 100644
--- a/arch/um/os-Linux/signal.c
+++ b/arch/um/os-Linux/signal.c
@@ -55,7 +55,15 @@ 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);
@@ -69,6 +77,12 @@ static void sig_handler_common(int sig, struct siginfo *si,
mcontext_t *mc)
(*sig_info[sig])(sig, si, &r);
errno = save_errno;
+
+#ifndef CONFIG_MMU
+ /* force handle signals after rt_sigreturn() */
+ if (r.is_user && sig == SIGSEGV)
+ mc_set_regs_ip_relay(mc);
+#endif
}
/*
diff --git a/arch/x86/um/signal.c b/arch/x86/um/signal.c
index 75087e85b6fd..e1b3a87ddc5d 100644
--- a/arch/x86/um/signal.c
+++ b/arch/x86/um/signal.c
@@ -370,6 +370,13 @@ int setup_signal_stack_si(unsigned long stack_top, struct
ksignal *ksig,
frame = (struct rt_sigframe __user *)
round_down(stack_top - sizeof(struct rt_sigframe), 16);
+#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
/* Add required space for math frame */
frame = (struct rt_sigframe __user *)((unsigned long)frame - math_size);
@@ -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
