This commit updates the behavior of signal handling under !MMU
environment. It adds the alignment code for signal frame as the frame
is used in userspace as-is.
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/nommu/Makefile | 2 +-
arch/um/nommu/trap.c | 188 ++++++++++++++++++++++++++
arch/um/os-Linux/signal.c | 6 +
arch/x86/um/nommu/os-Linux/mcontext.c | 11 ++
arch/x86/um/shared/sysdep/mcontext.h | 1 +
arch/x86/um/signal.c | 7 +
6 files changed, 214 insertions(+), 1 deletion(-)
create mode 100644 arch/um/nommu/trap.c
diff --git a/arch/um/nommu/Makefile b/arch/um/nommu/Makefile
index baab7c2f57c2..096221590cfd 100644
--- a/arch/um/nommu/Makefile
+++ b/arch/um/nommu/Makefile
@@ -1,3 +1,3 @@
# SPDX-License-Identifier: GPL-2.0
-obj-y := os-Linux/
+obj-y := trap.o os-Linux/
diff --git a/arch/um/nommu/trap.c b/arch/um/nommu/trap.c
new file mode 100644
index 000000000000..cda71ecb1115
--- /dev/null
+++ b/arch/um/nommu/trap.c
@@ -0,0 +1,188 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/mm.h>
+#include <linux/sched/signal.h>
+#include <linux/hardirq.h>
+#include <linux/module.h>
+#include <linux/uaccess.h>
+#include <linux/sched/debug.h>
+#include <asm/current.h>
+#include <asm/tlbflush.h>
+#include <arch.h>
+#include <as-layout.h>
+#include <kern_util.h>
+#include <os.h>
+#include <skas.h>
+
+/*
+ * Note this is constrained to return 0, -EFAULT, -EACCES, -ENOMEM by
+ * segv().
+ */
+int handle_page_fault(unsigned long address, unsigned long ip,
+ int is_write, int is_user, int *code_out)
+{
+ /* !MMU has no pagefault */
+ return -EFAULT;
+}
+
+static void show_segv_info(struct uml_pt_regs *regs)
+{
+ struct task_struct *tsk = current;
+ struct faultinfo *fi = UPT_FAULTINFO(regs);
+
+ if (!unhandled_signal(tsk, SIGSEGV))
+ return;
+
+ pr_warn_ratelimited("%s%s[%d]: segfault at %lx ip %p sp %p error %x",
+ task_pid_nr(tsk) > 1 ? KERN_INFO : KERN_EMERG,
+ tsk->comm, task_pid_nr(tsk), FAULT_ADDRESS(*fi),
+ (void *)UPT_IP(regs), (void *)UPT_SP(regs),
+ fi->error_code);
+}
+
+static void bad_segv(struct faultinfo fi, unsigned long ip)
+{
+ current->thread.arch.faultinfo = fi;
+ force_sig_fault(SIGSEGV, SEGV_ACCERR, (void __user *)
FAULT_ADDRESS(fi));
+}
+
+void fatal_sigsegv(void)
+{
+ force_fatal_sig(SIGSEGV);
+ do_signal(¤t->thread.regs);
+ /*
+ * This is to tell gcc that we're not returning - do_signal
+ * can, in general, return, but in this case, it's not, since
+ * we just got a fatal SIGSEGV queued.
+ */
+ os_dump_core();
+}
+
+/**
+ * segv_handler() - the SIGSEGV handler
+ * @sig: the signal number
+ * @unused_si: the signal info struct; unused in this handler
+ * @regs: the ptrace register information
+ *
+ * The handler first extracts the faultinfo from the UML ptrace regs struct.
+ * If the userfault did not happen in an UML userspace process, bad_segv is
called.
+ * Otherwise the signal did happen in a cloned userspace process, handle it.
+ */
+void segv_handler(int sig, struct siginfo *unused_si, struct uml_pt_regs *regs)
+{
+ struct faultinfo *fi = UPT_FAULTINFO(regs);
+
+ /* !MMU specific part; detection of userspace */
+ /* mark is_user=1 when the IP is from userspace code. */
+ if (UPT_IP(regs) > uml_reserved && UPT_IP(regs) < high_physmem)
+ regs->is_user = 1;
+
+ if (UPT_IS_USER(regs) && !SEGV_IS_FIXABLE(fi)) {
+ show_segv_info(regs);
+ bad_segv(*fi, UPT_IP(regs));
+ return;
+ }
+ segv(*fi, UPT_IP(regs), UPT_IS_USER(regs), regs);
+}
+
+/*
+ * We give a *copy* of the faultinfo in the regs to segv.
+ * This must be done, since nesting SEGVs could overwrite
+ * the info in the regs. A pointer to the info then would
+ * give us bad data!
+ */
+unsigned long segv(struct faultinfo fi, unsigned long ip, int is_user,
+ struct uml_pt_regs *regs)
+{
+ int si_code;
+ int err;
+ int is_write = FAULT_WRITE(fi);
+ unsigned long address = FAULT_ADDRESS(fi);
+
+ if (!is_user && regs)
+ current->thread.segv_regs = container_of(regs, struct pt_regs,
regs);
+
+ if (current->mm == NULL) {
+ show_regs(container_of(regs, struct pt_regs, regs));
+ panic("Segfault with no mm");
+ } else if (!is_user && address > PAGE_SIZE && address < TASK_SIZE) {
+ show_regs(container_of(regs, struct pt_regs, regs));
+ panic("Kernel tried to access user memory at addr 0x%lx, ip
0x%lx",
+ address, ip);
+ }
+
+ if (SEGV_IS_FIXABLE(&fi))
+ err = handle_page_fault(address, ip, is_write, is_user,
+ &si_code);
+ else {
+ err = -EFAULT;
+ /*
+ * A thread accessed NULL, we get a fault, but CR2 is invalid.
+ * This code is used in __do_copy_from_user() of TT mode.
+ * XXX tt mode is gone, so maybe this isn't needed any more
+ */
+ address = 0;
+ }
+
+ if (!err)
+ goto out;
+ else if (!is_user && arch_fixup(ip, regs))
+ goto out;
+
+ if (!is_user) {
+ show_regs(container_of(regs, struct pt_regs, regs));
+ panic("Kernel mode fault at addr 0x%lx, ip 0x%lx",
+ address, ip);
+ }
+
+ show_segv_info(regs);
+
+ if (err == -EACCES) {
+ current->thread.arch.faultinfo = fi;
+ force_sig_fault(SIGBUS, BUS_ADRERR, (void __user *)address);
+ } else {
+ WARN_ON_ONCE(err != -EFAULT);
+ current->thread.arch.faultinfo = fi;
+ force_sig_fault(SIGSEGV, si_code, (void __user *) address);
+ }
+
+out:
+ if (regs)
+ current->thread.segv_regs = NULL;
+
+ return 0;
+}
+
+void relay_signal(int sig, struct siginfo *si, struct uml_pt_regs *regs)
+{
+ int code, err;
+
+ if (!UPT_IS_USER(regs)) {
+ if (sig == SIGBUS)
+ pr_err("Bus error - the host /dev/shm or /tmp mount
likely just ran out of space\n");
+ panic("Kernel mode signal %d", sig);
+ }
+
+ arch_examine_signal(sig, regs);
+
+ /* Is the signal layout for the signal known?
+ * Signal data must be scrubbed to prevent information leaks.
+ */
+ code = si->si_code;
+ err = si->si_errno;
+ if ((err == 0) && (siginfo_layout(sig, code) == SIL_FAULT)) {
+ struct faultinfo *fi = UPT_FAULTINFO(regs);
+
+ current->thread.arch.faultinfo = *fi;
+ force_sig_fault(sig, code, (void __user *)FAULT_ADDRESS(*fi));
+ } else {
+ pr_err("Attempted to relay unknown signal %d (si_code = %d)
with errno %d\n",
+ sig, code, err);
+ force_sig(sig);
+ }
+}
+
+void winch(int sig, struct siginfo *unused_si, struct uml_pt_regs *regs)
+{
+ do_IRQ(WINCH_IRQ, regs);
+}
diff --git a/arch/um/os-Linux/signal.c b/arch/um/os-Linux/signal.c
index 97efdabe1e45..83e46c047f6c 100644
--- a/arch/um/os-Linux/signal.c
+++ b/arch/um/os-Linux/signal.c
@@ -50,6 +50,12 @@ 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
+ /* !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/nommu/os-Linux/mcontext.c
b/arch/x86/um/nommu/os-Linux/mcontext.c
index d74bc0726a28..cbb1cc4dabbb 100644
--- a/arch/x86/um/nommu/os-Linux/mcontext.c
+++ b/arch/x86/um/nommu/os-Linux/mcontext.c
@@ -6,6 +6,17 @@
#include <sysdep/mcontext.h>
#include <sysdep/syscalls.h>
+static void userspace_relay_signal(void)
+{
+ /* XXX: dummy syscall */
+ __asm__ volatile("call *%0" : : "r"(__kernel_vsyscall), "a"(39) :);
+}
+
+void mc_set_regs_ip_relay(mcontext_t *mc)
+{
+ mc->gregs[REG_RIP] = (unsigned long) userspace_relay_signal;
+}
+
void mc_set_sigsys_hook(mcontext_t *mc)
{
mc->gregs[REG_RCX] = mc->gregs[REG_RIP];
diff --git a/arch/x86/um/shared/sysdep/mcontext.h
b/arch/x86/um/shared/sysdep/mcontext.h
index 3f2dc3a2995c..0e837f4b5757 100644
--- a/arch/x86/um/shared/sysdep/mcontext.h
+++ b/arch/x86/um/shared/sysdep/mcontext.h
@@ -9,6 +9,7 @@
extern void get_regs_from_mc(struct uml_pt_regs *, mcontext_t *);
#ifndef CONFIG_MMU
extern void mc_set_sigsys_hook(mcontext_t *mc);
+extern void mc_set_regs_ip_relay(mcontext_t *mc);
#endif
#ifdef __i386__
diff --git a/arch/x86/um/signal.c b/arch/x86/um/signal.c
index 75087e85b6fd..ea6b408e37d2 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);
--
2.43.0
