[PATCH 00/20] exit cleanups

[PATCH 00/20] exit cleanups

[Eric W. Biederman]

While looking at some issues related to the exit path in the kernel I
found several instances where the code is not using the existing
abstractions properly.

This set of changes introduces force_fatal_sig a way of sending
a signal and not allowing it to be caught, and corrects the
misuse of the existing abstractions that I found.

A lot of the misuse of the existing abstractions are silly things such
as doing something after calling a no return function, rolling BUG by
hand, doing more work than necessary to terminate a kernel thread, or
calling do_exit(SIGKILL) instead of calling force_sig(SIGKILL).

It is my plan after sending all of these changes out for review to place
them in a topic branch for sending Linus.  Especially for the changes
that depend upon the new helper force_fatal_sig this is important.

Eric W. Biederman (20):
      exit/doublefault: Remove apparently bogus comment about rewind_stack_do_exit
      exit: Remove calls of do_exit after noreturn versions of die
      reboot: Remove the unreachable panic after do_exit in reboot(2)
      signal/sparc32: Remove unreachable do_exit in do_sparc_fault
      signal/mips: Update (_save|_restore)_fp_context to fail with -EFAULT
      signal/sh: Use force_sig(SIGKILL) instead of do_group_exit(SIGKILL)
      signal/powerpc: On swapcontext failure force SIGSEGV
      signal/sparc: In setup_tsb_params convert open coded BUG into BUG
      signal/vm86_32: Replace open coded BUG_ON with an actual BUG_ON
      signal/vm86_32: Properly send SIGSEGV when the vm86 state cannot be saved.
      signal/s390: Use force_sigsegv in default_trap_handler
      exit/kthread: Have kernel threads return instead of calling do_exit
      signal: Implement force_fatal_sig
      exit/syscall_user_dispatch: Send ordinary signals on failure
      signal/sparc32: Exit with a fatal signal when try_to_clear_window_buffer fails
      signal/sparc32: In setup_rt_frame and setup_fram use force_fatal_sig
      signal/x86: In emulate_vsyscall force a signal instead of calling do_exit
      exit/rtl8723bs: Replace the macro thread_exit with a simple return 0
      exit/rtl8712: Replace the macro thread_exit with a simple return 0
      exit/r8188eu: Replace the macro thread_exit with a simple return 0

 arch/mips/kernel/r2300_fpu.S                       |  4 ++--
 arch/mips/kernel/syscall.c                         |  9 --------
 arch/nds32/kernel/traps.c                          |  2 +-
 arch/nds32/mm/fault.c                              |  6 +----
 arch/openrisc/kernel/traps.c                       |  2 +-
 arch/openrisc/mm/fault.c                           |  4 +---
 arch/powerpc/kernel/signal_32.c                    |  6 +++--
 arch/powerpc/kernel/signal_64.c                    |  9 +++++---
 arch/s390/include/asm/kdebug.h                     |  2 +-
 arch/s390/kernel/dumpstack.c                       |  2 +-
 arch/s390/kernel/traps.c                           |  2 +-
 arch/s390/mm/fault.c                               |  2 --
 arch/sh/kernel/cpu/fpu.c                           | 10 +++++----
 arch/sh/kernel/traps.c                             |  2 +-
 arch/sh/mm/fault.c                                 |  2 --
 arch/sparc/kernel/signal_32.c                      |  4 ++--
 arch/sparc/kernel/windows.c                        |  6 +++--
 arch/sparc/mm/fault_32.c                           |  1 -
 arch/sparc/mm/tsb.c                                |  2 +-
 arch/x86/entry/vsyscall/vsyscall_64.c              |  3 ++-
 arch/x86/kernel/doublefault_32.c                   |  3 ---
 arch/x86/kernel/signal.c                           |  6 ++++-
 arch/x86/kernel/vm86_32.c                          |  8 +++----
 arch/xtensa/kernel/traps.c                         |  2 +-
 arch/xtensa/mm/fault.c                             |  3 +--
 drivers/firmware/stratix10-svc.c                   |  4 ++--
 drivers/soc/ti/wkup_m3_ipc.c                       |  2 +-
 drivers/staging/r8188eu/core/rtw_cmd.c             |  2 +-
 drivers/staging/r8188eu/core/rtw_mp.c              |  2 +-
 drivers/staging/r8188eu/include/osdep_service.h    |  2 --
 drivers/staging/rtl8712/osdep_service.h            |  1 -
 drivers/staging/rtl8712/rtl8712_cmd.c              |  2 +-
 drivers/staging/rtl8723bs/core/rtw_cmd.c           |  2 +-
 drivers/staging/rtl8723bs/core/rtw_xmit.c          |  2 +-
 drivers/staging/rtl8723bs/hal/rtl8723bs_xmit.c     |  2 +-
 .../rtl8723bs/include/osdep_service_linux.h        |  2 --
 fs/ocfs2/journal.c                                 |  5 +----
 include/linux/sched/signal.h                       |  1 +
 kernel/entry/syscall_user_dispatch.c               | 12 ++++++----
 kernel/kthread.c                                   |  2 +-
 kernel/reboot.c                                    |  1 -
 kernel/signal.c                                    | 26 ++++++++++++++--------
 net/batman-adv/tp_meter.c                          |  2 +-
 43 files changed, 83 insertions(+), 91 deletions(-)

Eric

[PATCH 07/20] signal/powerpc: On swapcontext failure force SIGSEGV

[Eric W. Biederman]

If the register state may be partial and corrupted instead of calling
do_exit, call force_sigsegv(SIGSEGV).  Which properly kills the
process with SIGSEGV and does not let any more userspace code execute,
instead of just killing one thread of the process and potentially
confusing everything.

Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: linuxppc-dev@lists.ozlabs.org
History-tree: git://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git
Fixes: 756f1ae8a44e ("PPC32: Rework signal code and add a swapcontext system call.")
Fixes: 04879b04bf50 ("[PATCH] ppc64: VMX (Altivec) support & signal32 rework, from Ben Herrenschmidt")
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
---
 arch/powerpc/kernel/signal_32.c | 6 ++++--
 arch/powerpc/kernel/signal_64.c | 9 ++++++---
 2 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/arch/powerpc/kernel/signal_32.c b/arch/powerpc/kernel/signal_32.c
index 0608581967f0..666f3da41232 100644
--- a/arch/powerpc/kernel/signal_32.c
+++ b/arch/powerpc/kernel/signal_32.c
@@ -1062,8 +1062,10 @@ SYSCALL_DEFINE3(swapcontext, struct ucontext __user *, old_ctx,
 	 * or if another thread unmaps the region containing the context.
 	 * We kill the task with a SIGSEGV in this situation.
 	 */
-	if (do_setcontext(new_ctx, regs, 0))
-		do_exit(SIGSEGV);
+	if (do_setcontext(new_ctx, regs, 0)) {
+		force_sigsegv(SIGSEGV);
+		return -EFAULT;
+	}
 
 	set_thread_flag(TIF_RESTOREALL);
 	return 0;
diff --git a/arch/powerpc/kernel/signal_64.c b/arch/powerpc/kernel/signal_64.c
index 1831bba0582e..d8de622c9e4a 100644
--- a/arch/powerpc/kernel/signal_64.c
+++ b/arch/powerpc/kernel/signal_64.c
@@ -703,15 +703,18 @@ SYSCALL_DEFINE3(swapcontext, struct ucontext __user *, old_ctx,
 	 * We kill the task with a SIGSEGV in this situation.
 	 */
 
-	if (__get_user_sigset(&set, &new_ctx->uc_sigmask))
-		do_exit(SIGSEGV);
+	if (__get_user_sigset(&set, &new_ctx->uc_sigmask)) {
+		force_sigsegv(SIGSEGV);
+		return -EFAULT;
+	}
 	set_current_blocked(&set);
 
 	if (!user_read_access_begin(new_ctx, ctx_size))
 		return -EFAULT;
 	if (__unsafe_restore_sigcontext(current, NULL, 0, &new_ctx->uc_mcontext)) {
 		user_read_access_end();
-		do_exit(SIGSEGV);
+		force_sigsegv(SIGSEGV);
+		return -EFAULT;
 	}
 	user_read_access_end();
 
-- 
2.20.1

Re: [PATCH 07/20] signal/powerpc: On swapcontext failure force SIGSEGV

[Kees Cook]

On Wed, Oct 20, 2021 at 12:43:53PM -0500, Eric W. Biederman wrote:
> If the register state may be partial and corrupted instead of calling
> do_exit, call force_sigsegv(SIGSEGV).  Which properly kills the
> process with SIGSEGV and does not let any more userspace code execute,
> instead of just killing one thread of the process and potentially
> confusing everything.
> 
> Cc: Michael Ellerman <mpe@ellerman.id.au>
> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> Cc: Paul Mackerras <paulus@samba.org>
> Cc: linuxppc-dev@lists.ozlabs.org
> History-tree: git://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git
> Fixes: 756f1ae8a44e ("PPC32: Rework signal code and add a swapcontext system call.")
> Fixes: 04879b04bf50 ("[PATCH] ppc64: VMX (Altivec) support & signal32 rework, from Ben Herrenschmidt")
> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

This looks right to me.

Reviewed-by: Kees Cook <keescook@chromium.org>

-- 
Kees Cook

[PATCH 21/20] signal: Replace force_sigsegv(SIGSEGV) with force_fatal_sig(SIGSEGV)

[Eric W. Biederman]

Now that force_fatal_sig exists it is unnecessary and a bit confusing
to use force_sigsegv in cases where the simpler force_fatal_sig is
wanted.  So change every instance we can to make the code clearer.

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
---
 arch/arc/kernel/process.c       | 2 +-
 arch/m68k/kernel/traps.c        | 2 +-
 arch/powerpc/kernel/signal_32.c | 2 +-
 arch/powerpc/kernel/signal_64.c | 4 ++--
 arch/s390/kernel/traps.c        | 2 +-
 arch/um/kernel/trap.c           | 2 +-
 arch/x86/kernel/vm86_32.c       | 2 +-
 fs/exec.c                       | 2 +-
 8 files changed, 9 insertions(+), 9 deletions(-)

diff --git a/arch/arc/kernel/process.c b/arch/arc/kernel/process.c
index 3793876f42d9..8e90052f6f05 100644
--- a/arch/arc/kernel/process.c
+++ b/arch/arc/kernel/process.c
@@ -294,7 +294,7 @@ int elf_check_arch(const struct elf32_hdr *x)
 	eflags = x->e_flags;
 	if ((eflags & EF_ARC_OSABI_MSK) != EF_ARC_OSABI_CURRENT) {
 		pr_err("ABI mismatch - you need newer toolchain\n");
-		force_sigsegv(SIGSEGV);
+		force_fatal_sig(SIGSEGV);
 		return 0;
 	}
 
diff --git a/arch/m68k/kernel/traps.c b/arch/m68k/kernel/traps.c
index 5b19fcdcd69e..74045d164ddb 100644
--- a/arch/m68k/kernel/traps.c
+++ b/arch/m68k/kernel/traps.c
@@ -1150,7 +1150,7 @@ asmlinkage void set_esp0(unsigned long ssp)
  */
 asmlinkage void fpsp040_die(void)
 {
-	force_sigsegv(SIGSEGV);
+	force_fatal_sig(SIGSEGV);
 }
 
 #ifdef CONFIG_M68KFPU_EMU
diff --git a/arch/powerpc/kernel/signal_32.c b/arch/powerpc/kernel/signal_32.c
index 666f3da41232..933ab95805a6 100644
--- a/arch/powerpc/kernel/signal_32.c
+++ b/arch/powerpc/kernel/signal_32.c
@@ -1063,7 +1063,7 @@ SYSCALL_DEFINE3(swapcontext, struct ucontext __user *, old_ctx,
 	 * We kill the task with a SIGSEGV in this situation.
 	 */
 	if (do_setcontext(new_ctx, regs, 0)) {
-		force_sigsegv(SIGSEGV);
+		force_fatal_sig(SIGSEGV);
 		return -EFAULT;
 	}
 
diff --git a/arch/powerpc/kernel/signal_64.c b/arch/powerpc/kernel/signal_64.c
index d8de622c9e4a..8ead9b3f47c6 100644
--- a/arch/powerpc/kernel/signal_64.c
+++ b/arch/powerpc/kernel/signal_64.c
@@ -704,7 +704,7 @@ SYSCALL_DEFINE3(swapcontext, struct ucontext __user *, old_ctx,
 	 */
 
 	if (__get_user_sigset(&set, &new_ctx->uc_sigmask)) {
-		force_sigsegv(SIGSEGV);
+		force_fatal_sig(SIGSEGV);
 		return -EFAULT;
 	}
 	set_current_blocked(&set);
@@ -713,7 +713,7 @@ SYSCALL_DEFINE3(swapcontext, struct ucontext __user *, old_ctx,
 		return -EFAULT;
 	if (__unsafe_restore_sigcontext(current, NULL, 0, &new_ctx->uc_mcontext)) {
 		user_read_access_end();
-		force_sigsegv(SIGSEGV);
+		force_fatal_sig(SIGSEGV);
 		return -EFAULT;
 	}
 	user_read_access_end();
diff --git a/arch/s390/kernel/traps.c b/arch/s390/kernel/traps.c
index 51729ea2cf8e..01a7c68dcfb6 100644
--- a/arch/s390/kernel/traps.c
+++ b/arch/s390/kernel/traps.c
@@ -84,7 +84,7 @@ static void default_trap_handler(struct pt_regs *regs)
 {
 	if (user_mode(regs)) {
 		report_user_fault(regs, SIGSEGV, 0);
-		force_sigsegv(SIGSEGV);
+		force_fatal_sig(SIGSEGV);
 	} else
 		die(regs, "Unknown program exception");
 }
diff --git a/arch/um/kernel/trap.c b/arch/um/kernel/trap.c
index 3198c4767387..c32efb09db21 100644
--- a/arch/um/kernel/trap.c
+++ b/arch/um/kernel/trap.c
@@ -158,7 +158,7 @@ static void bad_segv(struct faultinfo fi, unsigned long ip)
 
 void fatal_sigsegv(void)
 {
-	force_sigsegv(SIGSEGV);
+	force_fatal_sig(SIGSEGV);
 	do_signal(&current->thread.regs);
 	/*
 	 * This is to tell gcc that we're not returning - do_signal
diff --git a/arch/x86/kernel/vm86_32.c b/arch/x86/kernel/vm86_32.c
index 040fd01be8b3..7ff0f622abd4 100644
--- a/arch/x86/kernel/vm86_32.c
+++ b/arch/x86/kernel/vm86_32.c
@@ -159,7 +159,7 @@ void save_v86_state(struct kernel_vm86_regs *regs, int retval)
 	user_access_end();
 Efault:
 	pr_alert("could not access userspace vm86 info\n");
-	force_sigsegv(SIGSEGV);
+	force_fatal_sig(SIGSEGV);
 }
 
 static int do_vm86_irq_handling(int subfunction, int irqnumber);
diff --git a/fs/exec.c b/fs/exec.c
index a098c133d8d7..ac7b51b51f38 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1852,7 +1852,7 @@ static int bprm_execve(struct linux_binprm *bprm,
 	 * SIGSEGV.
 	 */
 	if (bprm->point_of_no_return && !fatal_signal_pending(current))
-		force_sigsegv(SIGSEGV);
+		force_fatal_sig(SIGSEGV);
 
 out_unmark:
 	current->fs->in_exec = 0;
-- 
2.20.1

Re: [PATCH 21/20] signal: Replace force_sigsegv(SIGSEGV) with force_fatal_sig(SIGSEGV)

[Geert Uytterhoeven]

Hi Eric,

Patch 21/20?

On Wed, Oct 20, 2021 at 11:52 PM Eric W. Biederman
<ebiederm@xmission.com> wrote:
> Now that force_fatal_sig exists it is unnecessary and a bit confusing
> to use force_sigsegv in cases where the simpler force_fatal_sig is
> wanted.  So change every instance we can to make the code clearer.
>
> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

>  arch/m68k/kernel/traps.c        | 2 +-

Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

Re: [PATCH 21/20] signal: Replace force_sigsegv(SIGSEGV) with force_fatal_sig(SIGSEGV)

[Eric W. Biederman]

Geert Uytterhoeven <geert@linux-m68k.org> writes:

> Hi Eric,
>
> Patch 21/20?

In reviewing another part of the patchset Linus asked if force_sigsegv
could go away.  It can't completely but I can get this far.

Given that it is just a cleanup it makes most sense to me as an
additional patch on top of what is already here.


> On Wed, Oct 20, 2021 at 11:52 PM Eric W. Biederman
> <ebiederm@xmission.com> wrote:
>> Now that force_fatal_sig exists it is unnecessary and a bit confusing
>> to use force_sigsegv in cases where the simpler force_fatal_sig is
>> wanted.  So change every instance we can to make the code clearer.
>>
>> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
>
>>  arch/m68k/kernel/traps.c        | 2 +-
>
> Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>

Thank you.

Eric

Re: [PATCH 21/20] signal: Replace force_sigsegv(SIGSEGV) with force_fatal_sig(SIGSEGV)

[Philippe Mathieu-Daudé]

On Wed, Oct 20, 2021 at 11:52 PM Eric W. Biederman
<ebiederm@xmission.com> wrote:
>
>
> Now that force_fatal_sig exists it is unnecessary and a bit confusing
> to use force_sigsegv in cases where the simpler force_fatal_sig is
> wanted.  So change every instance we can to make the code clearer.
>
> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
> ---
>  arch/arc/kernel/process.c       | 2 +-
>  arch/m68k/kernel/traps.c        | 2 +-
>  arch/powerpc/kernel/signal_32.c | 2 +-
>  arch/powerpc/kernel/signal_64.c | 4 ++--
>  arch/s390/kernel/traps.c        | 2 +-
>  arch/um/kernel/trap.c           | 2 +-
>  arch/x86/kernel/vm86_32.c       | 2 +-
>  fs/exec.c                       | 2 +-
>  8 files changed, 9 insertions(+), 9 deletions(-)

Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>