[PATCH 5.4.y] signal/m68k: Use force_sigsegv(SIGSEGV) in fpsp040_die

[PATCH 5.4.y] signal/m68k: Use force_sigsegv(SIGSEGV) in fpsp040_die

[Finn Thain]

From: "Eric W. Biederman" <ebiederm@xmission.com>

[ Upstream commit a3616a3c02722d1edb95acc7fceade242f6553ba ]

In the fpsp040 code when copyin or copyout fails call
force_sigsegv(SIGSEGV) instead of do_exit(SIGSEGV).

This solves a couple of problems.  Because do_exit embeds the ptrace
stop PTRACE_EVENT_EXIT a complete stack frame needs to be present for
that to work correctly.  There is always the information needed for a
ptrace stop where get_signal is called.  So exiting with a signal
solves the ptrace issue.

Further exiting with a signal ensures that all of the threads in a
process are killed not just the thread that malfunctioned.  Which
avoids confusing userspace.

To make force_sigsegv(SIGSEGV) work in fpsp040_die modify the code to
save all of the registers and jump to ret_from_exception (which
ultimately calls get_signal) after fpsp040_die returns.

v2: Updated the branches to use gas's pseudo ops that automatically
    calculate the best branch instruction to use for the purpose.

v1: https://lkml.kernel.org/r/87a6m8kgtx.fsf_-_@disp2133
Link: https://lkml.kernel.org/r/87tukghjfs.fsf_-_@disp2133
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Finn Thain <fthain@linux-m68k.org>
---
 arch/m68k/fpsp040/skeleton.S | 3 ++-
 arch/m68k/kernel/traps.c     | 2 +-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/m68k/fpsp040/skeleton.S b/arch/m68k/fpsp040/skeleton.S
index 31a9c634c81e..081922c72daa 100644
--- a/arch/m68k/fpsp040/skeleton.S
+++ b/arch/m68k/fpsp040/skeleton.S
@@ -502,7 +502,8 @@ in_ea:
 	.section .fixup,"ax"
 	.even
 1:
-	jbra	fpsp040_die
+	jbsr	fpsp040_die
+	jbra	.Lnotkern
 
 	.section __ex_table,"a"
 	.align	4
diff --git a/arch/m68k/kernel/traps.c b/arch/m68k/kernel/traps.c
index 35f706d836c5..c6f18dc5884b 100644
--- a/arch/m68k/kernel/traps.c
+++ b/arch/m68k/kernel/traps.c
@@ -1155,7 +1155,7 @@ asmlinkage void set_esp0(unsigned long ssp)
  */
 asmlinkage void fpsp040_die(void)
 {
-	do_exit(SIGSEGV);
+	force_sigsegv(SIGSEGV);
 }
 
 #ifdef CONFIG_M68KFPU_EMU

Re: [PATCH 5.4.y] signal/m68k: Use force_sigsegv(SIGSEGV) in fpsp040_die

[Sasha Levin]

[ Sasha's backport helper bot ]

Hi,

The upstream commit SHA1 provided is correct: a3616a3c02722d1edb95acc7fceade242f6553ba

WARNING: Author mismatch between patch and upstream commit:
Backport author: Finn Thain<fthain@linux-m68k.org>
Commit author: Eric W. Biederman<ebiederm@xmission.com>


Status in newer kernel trees:
6.12.y | Present (exact SHA1)
6.6.y | Present (exact SHA1)
6.1.y | Present (exact SHA1)
5.15.y | Present (exact SHA1)
5.10.y | Not found
5.4.y | Not found

Note: The patch differs from the upstream commit:
---
1:  a3616a3c02722 ! 1:  bf9f85b11138f signal/m68k: Use force_sigsegv(SIGSEGV) in fpsp040_die
    @@ Metadata
      ## Commit message ##
         signal/m68k: Use force_sigsegv(SIGSEGV) in fpsp040_die
     
    +    [ Upstream commit a3616a3c02722d1edb95acc7fceade242f6553ba ]
    +
         In the fpsp040 code when copyin or copyout fails call
         force_sigsegv(SIGSEGV) instead of do_exit(SIGSEGV).
     
    @@ Commit message
         Link: https://lkml.kernel.org/r/87tukghjfs.fsf_-_@disp2133
         Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>
         Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
    +    Signed-off-by: Finn Thain <fthain@linux-m68k.org>
     
      ## arch/m68k/fpsp040/skeleton.S ##
     @@ arch/m68k/fpsp040/skeleton.S: in_ea:
    - 	.section .fixup,#alloc,#execinstr
    + 	.section .fixup,"ax"
      	.even
      1:
     -	jbra	fpsp040_die
     +	jbsr	fpsp040_die
     +	jbra	.Lnotkern
      
    - 	.section __ex_table,#alloc
    + 	.section __ex_table,"a"
      	.align	4
     
      ## arch/m68k/kernel/traps.c ##
---

Results of testing on various branches:

| Branch                    | Patch Apply | Build Test |
|---------------------------|-------------|------------|
| stable/linux-5.4.y        |  Success    |  Success   |