[PATCH 5.10.y] m68k: Update ->thread.esp0 before calling syscall_trace() in ret_from_signal

[PATCH 5.10.y] m68k: Update ->thread.esp0 before calling syscall_trace() in ret_from_signal

[Finn Thain]

From: Al Viro <viro@zeniv.linux.org.uk>

[ Upstream commit 50e43a57334400668952f8e551c9d87d3ed2dfef ]

We get there when sigreturn has performed obscene acts on kernel stack;
in particular, the location of pt_regs has shifted.  We are about to call
syscall_trace(), which might stop for tracer.  If that happens, we'd better
have task_pt_regs() returning correct result...

Fucked-up-by: Al Viro <viro@zeniv.linux.org.uk>
Fixes: bd6f56a75bb2 ("m68k: Missing syscall_trace() on sigreturn")
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Tested-by: Michael Schmitz <schmitzmic@gmail.com>
Reviewed-by: Michael Schmitz <schmitzmic@gmail.com>
Tested-by: Finn Thain <fthain@linux-m68k.org>
Link: https://lore.kernel.org/r/YP2dMWeV1LkHiOpr@zeniv-ca.linux.org.uk
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Finn Thain <fthain@linux-m68k.org>
---
 arch/m68k/kernel/entry.S | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/m68k/kernel/entry.S b/arch/m68k/kernel/entry.S
index 417d8f0e8962..0d03b4f2077b 100644
--- a/arch/m68k/kernel/entry.S
+++ b/arch/m68k/kernel/entry.S
@@ -182,6 +182,8 @@ ENTRY(ret_from_signal)
 	movel	%curptr@(TASK_STACK),%a1
 	tstb	%a1@(TINFO_FLAGS+2)
 	jge	1f
+	lea	%sp@(SWITCH_STACK_SIZE),%a1
+	movel	%a1,%curptr@(TASK_THREAD+THREAD_ESP0)
 	jbsr	syscall_trace
 1:	RESTORE_SWITCH_STACK
 	addql	#4,%sp

Re: [PATCH 5.10.y] m68k: Update ->thread.esp0 before calling syscall_trace() in ret_from_signal

[Sasha Levin]

[ Sasha's backport helper bot ]

Hi,

The upstream commit SHA1 provided is correct: 50e43a57334400668952f8e551c9d87d3ed2dfef

WARNING: Author mismatch between patch and upstream commit:
Backport author: Finn Thain<fthain@linux-m68k.org>
Commit author: Al Viro<viro@zeniv.linux.org.uk>


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

Note: The patch differs from the upstream commit:
---
1:  50e43a5733440 ! 1:  b38019d2d357f m68k: Update ->thread.esp0 before calling syscall_trace() in ret_from_signal
    @@ Metadata
      ## Commit message ##
         m68k: Update ->thread.esp0 before calling syscall_trace() in ret_from_signal
     
    +    [ Upstream commit 50e43a57334400668952f8e551c9d87d3ed2dfef ]
    +
         We get there when sigreturn has performed obscene acts on kernel stack;
         in particular, the location of pt_regs has shifted.  We are about to call
         syscall_trace(), which might stop for tracer.  If that happens, we'd better
    @@ Commit message
         Tested-by: Finn Thain <fthain@linux-m68k.org>
         Link: https://lore.kernel.org/r/YP2dMWeV1LkHiOpr@zeniv-ca.linux.org.uk
         Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
    +    Signed-off-by: Finn Thain <fthain@linux-m68k.org>
     
      ## arch/m68k/kernel/entry.S ##
     @@ arch/m68k/kernel/entry.S: ENTRY(ret_from_signal)
---

Results of testing on various branches:

| Branch                    | Patch Apply | Build Test |
|---------------------------|-------------|------------|
| stable/linux-5.10.y       |  Success    |  Success   |