[PATCH RFC 0/4]

[PATCH RFC 0/4]

[Michael Schmitz]

CIP v4.4 backport of Al Viro's misc. m68k signal handling and
page fault fixes. 

The first three are a prerequisite for Finn Thain's 'm68k: Move
signal frame following exception on 68020/030' patch, and fix
the backport compile error seen in 
https://lore.kernel.org/oe-kbuild-all/202401310920.sBSI4BHj-lkp@intel.com/

RFC version of these patches to give Geert and Al a chance to yell
at me in case I got details of these patches wrong. I don't claim
to understand signal handling in anywhere near the required level
of detail.

Tested on my 68030 Atari Falcon.

Cheers,

   Michael
   

[PATCH RFC 1/4] m68k: Handle arrivals of multiple signals correctly

[Michael Schmitz]

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

When we have several pending signals, have entered with the kernel
with large exception frame *and* have already built at least one
sigframe, regs->stkadj is going to be non-zero and regs->format/sr/pc
are going to be junk - the real values are in shifted exception stack
frame we'd built when putting together the first sigframe.

If that happens, subsequent sigframes are going to be garbage.
Not hard to fix - just need to find the "adjusted" frame first
and look for format/vector/sr/pc in it.

Minor merge conflict fixes for v4.4 added.

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/YP2dBIAPTaVvHiZ6@zeniv-ca.linux.org.uk
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
---
 arch/m68k/kernel/signal.c | 100 +++++++++++++++++---------------------
 1 file changed, 45 insertions(+), 55 deletions(-)

diff --git a/arch/m68k/kernel/signal.c b/arch/m68k/kernel/signal.c
index af1c4f330aef..644c2ddc8aac 100644
--- a/arch/m68k/kernel/signal.c
+++ b/arch/m68k/kernel/signal.c
@@ -465,7 +465,7 @@ static inline void save_fpu_state(struct sigcontext *sc, struct pt_regs *regs)
 
 	if (CPU_IS_060 ? sc->sc_fpstate[2] : sc->sc_fpstate[0]) {
 		fpu_version = sc->sc_fpstate[0];
-		if (CPU_IS_020_OR_030 &&
+		if (CPU_IS_020_OR_030 && !regs->stkadj &&
 		    regs->vector >= (VEC_FPBRUC * 4) &&
 		    regs->vector <= (VEC_FPNAN * 4)) {
 			/* Clear pending exception in 68882 idle frame */
@@ -528,7 +528,7 @@ static inline int rt_save_fpu_state(struct ucontext __user *uc, struct pt_regs *
 		if (!(CPU_IS_060 || CPU_IS_COLDFIRE))
 			context_size = fpstate[1];
 		fpu_version = fpstate[0];
-		if (CPU_IS_020_OR_030 &&
+		if (CPU_IS_020_OR_030 && !regs->stkadj &&
 		    regs->vector >= (VEC_FPBRUC * 4) &&
 		    regs->vector <= (VEC_FPNAN * 4)) {
 			/* Clear pending exception in 68882 idle frame */
@@ -788,18 +788,24 @@ badframe:
 	return 0;
 }
 
+static inline struct pt_regs *rte_regs(struct pt_regs *regs)
+{
+	return (void *)regs + regs->stkadj;
+}
+
 static void setup_sigcontext(struct sigcontext *sc, struct pt_regs *regs,
 			     unsigned long mask)
 {
+	struct pt_regs *tregs = rte_regs(regs);
 	sc->sc_mask = mask;
 	sc->sc_usp = rdusp();
 	sc->sc_d0 = regs->d0;
 	sc->sc_d1 = regs->d1;
 	sc->sc_a0 = regs->a0;
 	sc->sc_a1 = regs->a1;
-	sc->sc_sr = regs->sr;
-	sc->sc_pc = regs->pc;
-	sc->sc_formatvec = regs->format << 12 | regs->vector;
+	sc->sc_sr = tregs->sr;
+	sc->sc_pc = tregs->pc;
+	sc->sc_formatvec = tregs->format << 12 | tregs->vector;
 	save_a5_state(sc, regs);
 	save_fpu_state(sc, regs);
 }
@@ -807,6 +813,7 @@ static void setup_sigcontext(struct sigcontext *sc, struct pt_regs *regs,
 static inline int rt_setup_ucontext(struct ucontext __user *uc, struct pt_regs *regs)
 {
 	struct switch_stack *sw = (struct switch_stack *)regs - 1;
+	struct pt_regs *tregs = rte_regs(regs);
 	greg_t __user *gregs = uc->uc_mcontext.gregs;
 	int err = 0;
 
@@ -827,9 +834,9 @@ static inline int rt_setup_ucontext(struct ucontext __user *uc, struct pt_regs *
 	err |= __put_user(sw->a5, &gregs[13]);
 	err |= __put_user(sw->a6, &gregs[14]);
 	err |= __put_user(rdusp(), &gregs[15]);
-	err |= __put_user(regs->pc, &gregs[16]);
-	err |= __put_user(regs->sr, &gregs[17]);
-	err |= __put_user((regs->format << 12) | regs->vector, &uc->uc_formatvec);
+	err |= __put_user(tregs->pc, &gregs[16]);
+	err |= __put_user(tregs->sr, &gregs[17]);
+	err |= __put_user((tregs->format << 12) | tregs->vector, &uc->uc_formatvec);
 	err |= rt_save_fpu_state(uc, regs);
 	return err;
 }
@@ -846,15 +853,14 @@ static int setup_frame(struct ksignal *ksig, sigset_t *set,
 			struct pt_regs *regs)
 {
 	struct sigframe __user *frame;
-	int fsize = frame_extra_sizes(regs->format);
+	struct pt_regs *tregs = rte_regs(regs);
+	int fsize = frame_extra_sizes(tregs->format);
 	struct sigcontext context;
 	int err = 0, sig = ksig->sig;
 
 	if (fsize < 0) {
-#ifdef DEBUG
-		printk ("setup_frame: Unknown frame format %#x\n",
-			regs->format);
-#endif
+		pr_debug("setup_frame: Unknown frame format %#x\n",
+			 tregs->format);
 		return -EFAULT;
 	}
 
@@ -865,7 +871,7 @@ static int setup_frame(struct ksignal *ksig, sigset_t *set,
 
 	err |= __put_user(sig, &frame->sig);
 
-	err |= __put_user(regs->vector, &frame->code);
+	err |= __put_user(tregs->vector, &frame->code);
 	err |= __put_user(&frame->sc, &frame->psc);
 
 	if (_NSIG_WORDS > 1)
@@ -890,36 +896,28 @@ static int setup_frame(struct ksignal *ksig, sigset_t *set,
 
 	push_cache ((unsigned long) &frame->retcode);
 
-	/*
-	 * Set up registers for signal handler.  All the state we are about
-	 * to destroy is successfully copied to sigframe.
-	 */
-	wrusp ((unsigned long) frame);
-	regs->pc = (unsigned long) ksig->ka.sa.sa_handler;
-	adjustformat(regs);
-
 	/*
 	 * This is subtle; if we build more than one sigframe, all but the
 	 * first one will see frame format 0 and have fsize == 0, so we won't
 	 * screw stkadj.
 	 */
-	if (fsize)
+	if (fsize) {
 		regs->stkadj = fsize;
-
-	/* Prepare to skip over the extra stuff in the exception frame.  */
-	if (regs->stkadj) {
-		struct pt_regs *tregs =
-			(struct pt_regs *)((ulong)regs + regs->stkadj);
-#ifdef DEBUG
-		printk("Performing stackadjust=%04x\n", regs->stkadj);
-#endif
-		/* This must be copied with decreasing addresses to
-                   handle overlaps.  */
+		tregs = rte_regs(regs);
+		pr_debug("Performing stackadjust=%04lx\n", regs->stkadj);
 		tregs->vector = 0;
 		tregs->format = 0;
-		tregs->pc = regs->pc;
 		tregs->sr = regs->sr;
 	}
+
+	/*
+	 * Set up registers for signal handler.  All the state we are about
+	 * to destroy is successfully copied to sigframe.
+	 */
+	wrusp ((unsigned long) frame);
+	tregs->pc = (unsigned long) ksig->ka.sa.sa_handler;
+	adjustformat(regs);
+
 	return 0;
 }
 
@@ -927,7 +925,8 @@ static int setup_rt_frame(struct ksignal *ksig, sigset_t *set,
 			   struct pt_regs *regs)
 {
 	struct rt_sigframe __user *frame;
-	int fsize = frame_extra_sizes(regs->format);
+	struct pt_regs *tregs = rte_regs(regs);
+	int fsize = frame_extra_sizes(tregs->format);
 	int err = 0, sig = ksig->sig;
 
 	if (fsize < 0) {
@@ -978,36 +977,27 @@ static int setup_rt_frame(struct ksignal *ksig, sigset_t *set,
 
 	push_cache ((unsigned long) &frame->retcode);
 
-	/*
-	 * Set up registers for signal handler.  All the state we are about
-	 * to destroy is successfully copied to sigframe.
-	 */
-	wrusp ((unsigned long) frame);
-	regs->pc = (unsigned long) ksig->ka.sa.sa_handler;
-	adjustformat(regs);
-
 	/*
 	 * This is subtle; if we build more than one sigframe, all but the
 	 * first one will see frame format 0 and have fsize == 0, so we won't
 	 * screw stkadj.
 	 */
-	if (fsize)
+	if (fsize) {
 		regs->stkadj = fsize;
-
-	/* Prepare to skip over the extra stuff in the exception frame.  */
-	if (regs->stkadj) {
-		struct pt_regs *tregs =
-			(struct pt_regs *)((ulong)regs + regs->stkadj);
-#ifdef DEBUG
-		printk("Performing stackadjust=%04x\n", regs->stkadj);
-#endif
-		/* This must be copied with decreasing addresses to
-                   handle overlaps.  */
+		tregs = rte_regs(regs);
+		pr_debug("Performing stackadjust=%04lx\n", regs->stkadj);
 		tregs->vector = 0;
 		tregs->format = 0;
-		tregs->pc = regs->pc;
 		tregs->sr = regs->sr;
 	}
+
+	/*
+	 * Set up registers for signal handler.  All the state we are about
+	 * to destroy is successfully copied to sigframe.
+	 */
+	wrusp ((unsigned long) frame);
+	tregs->pc = (unsigned long) ksig->ka.sa.sa_handler;
+	adjustformat(regs);
 	return 0;
 }
 
-- 
2.17.1

[PATCH RFC 2/4] m68k: Update ->thread.esp0 before calling syscall_trace() in ret_from_signal

[Michael Schmitz]

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

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>
---
 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 b54ac7aba850..dbeba043b703 100644
--- a/arch/m68k/kernel/entry.S
+++ b/arch/m68k/kernel/entry.S
@@ -173,6 +173,8 @@ 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
-- 
2.17.1

[PATCH RFC 3/4] m68k: Leave stack mangling to asm wrapper of sigreturn()

[Michael Schmitz]

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

sigreturn has to deal with an unpleasant problem - exception stack frames
have different sizes, depending upon the exception (and processor model, as
well) and variable-sized part of exception frame may contain information
needed for instruction restart.  So when signal handler terminates and calls
sigreturn to resume the execution at the place where we'd been when we caught
the signal, it has to rearrange the frame at the bottom of kernel stack.
Worse, it might need to open a gap in the kernel stack, shifting pt_regs
towards lower addresses.

Doing that from C is insane - we'd need to shift stack frames (return addresses,
local variables, etc.) of C call chain, right under the nose of compiler and
hope it won't fall apart horribly.  What had been actually done is only slightly
less insane - an inline asm in mangle_kernel_stack() moved the stuff around,
then reset stack pointer and jumped to label in asm glue.

However, we can avoid all that mess if the asm wrapper we have to use anyway
would reserve some space on the stack between switch_stack and the C stack
frame of do_{rt_,}sigreturn().   Then C part can simply memmove() pt_regs +
switch_stack, memcpy() the variable part of exception frame into the opened
gap - all of that without inline asm, buggering C call chain, magical jumps
to asm labels, etc.

Asm wrapper would need to know where the moved switch_stack has ended up -
it might have been shifted into the gap we'd reserved before do_rt_sigreturn()
call.  That's where it needs to set the stack pointer to.  So let the C part
return just that and be done with that.

While we are at it, the call of berr_040cleanup() we need to do when
returning via 68040 bus error exception frame can be moved into C part
as well.

MSch: Minor v4.4 backport merge conflict and compile errors fixed.

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/YP2dTQPm1wGPWFgD@zeniv-ca.linux.org.uk
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Michael Schmitz <schmitzmic@gmail.com>
---
 arch/m68k/68000/entry.S       |   3 -
 arch/m68k/coldfire/entry.S    |   3 -
 arch/m68k/include/asm/traps.h |   4 ++
 arch/m68k/kernel/entry.S      |  49 +++++++-------
 arch/m68k/kernel/signal.c     | 118 ++++++++++++----------------------
 5 files changed, 72 insertions(+), 105 deletions(-)

diff --git a/arch/m68k/68000/entry.S b/arch/m68k/68000/entry.S
index 259b3661b614..cce465e850fe 100644
--- a/arch/m68k/68000/entry.S
+++ b/arch/m68k/68000/entry.S
@@ -25,7 +25,6 @@
 .globl system_call
 .globl resume
 .globl ret_from_exception
-.globl ret_from_signal
 .globl sys_call_table
 .globl bad_interrupt
 .globl inthandler1
@@ -59,8 +58,6 @@ do_trace:
 	subql	#4,%sp			/* dummy return address */
 	SAVE_SWITCH_STACK
 	jbsr	syscall_trace_leave
-
-ret_from_signal:
 	RESTORE_SWITCH_STACK
 	addql	#4,%sp
 	jra	ret_from_exception
diff --git a/arch/m68k/coldfire/entry.S b/arch/m68k/coldfire/entry.S
index 52d312d5b4d4..1a75c1015847 100644
--- a/arch/m68k/coldfire/entry.S
+++ b/arch/m68k/coldfire/entry.S
@@ -51,7 +51,6 @@ sw_usp:
 .globl system_call
 .globl resume
 .globl ret_from_exception
-.globl ret_from_signal
 .globl sys_call_table
 .globl inthandler
 
@@ -98,8 +97,6 @@ ENTRY(system_call)
 	subql	#4,%sp			/* dummy return address */
 	SAVE_SWITCH_STACK
 	jbsr	syscall_trace_leave
-
-ret_from_signal:
 	RESTORE_SWITCH_STACK
 	addql	#4,%sp
 
diff --git a/arch/m68k/include/asm/traps.h b/arch/m68k/include/asm/traps.h
index 4aff3358fbaf..a9d5c1c870d3 100644
--- a/arch/m68k/include/asm/traps.h
+++ b/arch/m68k/include/asm/traps.h
@@ -267,6 +267,10 @@ struct frame {
     } un;
 };
 
+#ifdef CONFIG_M68040
+asmlinkage void berr_040cleanup(struct frame *fp);
+#endif
+
 #endif /* __ASSEMBLY__ */
 
 #endif /* _M68K_TRAPS_H */
diff --git a/arch/m68k/kernel/entry.S b/arch/m68k/kernel/entry.S
index dbeba043b703..9a79733b20db 100644
--- a/arch/m68k/kernel/entry.S
+++ b/arch/m68k/kernel/entry.S
@@ -71,14 +71,38 @@ ENTRY(__sys_vfork)
 
 ENTRY(sys_sigreturn)
 	SAVE_SWITCH_STACK
+	movel	%sp,%a1			  	| switch_stack pointer
+	lea	%sp@(SWITCH_STACK_SIZE),%a0	| pt_regs pointer
+	lea     %sp@(-84),%sp			| leave a gap
+	movel	%a1,%sp@-
+	movel	%a0,%sp@-
 	jbsr	do_sigreturn
-	RESTORE_SWITCH_STACK
-	rts
+	jra	1f				| shared with rt_sigreturn()
 
 ENTRY(sys_rt_sigreturn)
 	SAVE_SWITCH_STACK
+	movel	%sp,%a1			  	| switch_stack pointer
+	lea	%sp@(SWITCH_STACK_SIZE),%a0	| pt_regs pointer
+	lea     %sp@(-84),%sp			| leave a gap
+	movel	%a1,%sp@-
+	movel	%a0,%sp@-
+	| stack contents:
+	|   [original pt_regs address] [original switch_stack address]
+	|   [gap] [switch_stack] [pt_regs] [exception frame]
 	jbsr	do_rt_sigreturn
+
+1:
+	| stack contents now:
+	|   [original pt_regs address] [original switch_stack address]
+	|   [unused part of the gap] [moved switch_stack] [moved pt_regs]
+	|   [replacement exception frame]
+	| return value of do_{rt_,}sigreturn() points to moved switch_stack.
+
+	movel	%d0,%sp				| discard the leftover junk
 	RESTORE_SWITCH_STACK
+	| stack contents now is just [syscall return address] [pt_regs] [frame]
+	| return pt_regs.d0
+	movel	%sp@(PT_OFF_D0+4),%d0
 	rts
 
 ENTRY(buserr)
@@ -169,27 +193,6 @@ do_trace_exit:
 	addql	#4,%sp
 	jra	.Lret_from_exception
 
-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
-/* on 68040 complete pending writebacks if any */
-#ifdef CONFIG_M68040
-	bfextu	%sp@(PT_OFF_FORMATVEC){#0,#4},%d0
-	subql	#7,%d0				| bus error frame ?
-	jbne	1f
-	movel	%sp,%sp@-
-	jbsr	berr_040cleanup
-	addql	#4,%sp
-1:
-#endif
-	jra	.Lret_from_exception
-
 ENTRY(system_call)
 	SAVE_ALL_SYS
 
diff --git a/arch/m68k/kernel/signal.c b/arch/m68k/kernel/signal.c
index 644c2ddc8aac..8fb8ee804b3a 100644
--- a/arch/m68k/kernel/signal.c
+++ b/arch/m68k/kernel/signal.c
@@ -594,57 +594,35 @@ static inline int rt_save_fpu_state(struct ucontext __user *uc, struct pt_regs *
 static int mangle_kernel_stack(struct pt_regs *regs, int formatvec,
 			       void __user *fp)
 {
-	int fsize = frame_extra_sizes(formatvec >> 12);
-	if (fsize < 0) {
+	int extra = frame_extra_sizes(formatvec >> 12);
+	char buf[sizeof(((struct frame *)0)->un)];
+
+	if (extra < 0) {
 		/*
 		 * user process trying to return with weird frame format
 		 */
-#ifdef DEBUG
-		printk("user process returning with weird frame format\n");
-#endif
-		return 1;
+		pr_debug("user process returning with weird frame format\n");
+		return -1;
 	}
-	if (!fsize) {
-		regs->format = formatvec >> 12;
-		regs->vector = formatvec & 0xfff;
-	} else {
-		struct switch_stack *sw = (struct switch_stack *)regs - 1;
-		unsigned long buf[fsize / 2]; /* yes, twice as much */
-
-		/* that'll make sure that expansion won't crap over data */
-		if (copy_from_user(buf + fsize / 4, fp, fsize))
-			return 1;
-
-		/* point of no return */
-		regs->format = formatvec >> 12;
-		regs->vector = formatvec & 0xfff;
-#define frame_offset (sizeof(struct pt_regs)+sizeof(struct switch_stack))
-		__asm__ __volatile__ (
-#ifdef CONFIG_COLDFIRE
-			 "   movel %0,%/sp\n\t"
-			 "   bra ret_from_signal\n"
-#else
-			 "   movel %0,%/a0\n\t"
-			 "   subl %1,%/a0\n\t"     /* make room on stack */
-			 "   movel %/a0,%/sp\n\t"  /* set stack pointer */
-			 /* move switch_stack and pt_regs */
-			 "1: movel %0@+,%/a0@+\n\t"
-			 "   dbra %2,1b\n\t"
-			 "   lea %/sp@(%c3),%/a0\n\t" /* add offset of fmt */
-			 "   lsrl  #2,%1\n\t"
-			 "   subql #1,%1\n\t"
-			 /* copy to the gap we'd made */
-			 "2: movel %4@+,%/a0@+\n\t"
-			 "   dbra %1,2b\n\t"
-			 "   bral ret_from_signal\n"
+	if (extra && copy_from_user(buf, fp, extra))
+		return -1;
+	regs->format = formatvec >> 12;
+	regs->vector = formatvec & 0xfff;
+	if (extra) {
+		void *p = (struct switch_stack *)regs - 1;
+		struct frame *new = (void *)regs - extra;
+		int size = sizeof(struct pt_regs)+sizeof(struct switch_stack);
+
+		memmove(p - extra, p, size);
+		memcpy(p - extra + size, buf, extra);
+		current->thread.esp0 = (unsigned long)&new->ptregs;
+#ifdef CONFIG_M68040
+		/* on 68040 complete pending writebacks if any */
+		if (new->ptregs.format == 7) // bus error frame
+			berr_040cleanup(new);
 #endif
-			 : /* no outputs, it doesn't ever return */
-			 : "a" (sw), "d" (fsize), "d" (frame_offset/4-1),
-			   "n" (frame_offset), "a" (buf + fsize/4)
-			 : "a0");
-#undef frame_offset
 	}
-	return 0;
+	return extra;
 }
 
 static inline int
@@ -652,14 +630,13 @@ restore_sigcontext(struct pt_regs *regs, struct sigcontext __user *usc, void __u
 {
 	int formatvec;
 	struct sigcontext context;
-	int err = 0;
 
 	/* Always make any pending restarted system calls return -EINTR */
 	current->restart_block.fn = do_no_restart_syscall;
 
 	/* get previous context */
 	if (copy_from_user(&context, usc, sizeof(context)))
-		goto badframe;
+		return -1;
 
 	/* restore passed registers */
 	regs->d0 = context.sc_d0;
@@ -672,15 +649,10 @@ restore_sigcontext(struct pt_regs *regs, struct sigcontext __user *usc, void __u
 	wrusp(context.sc_usp);
 	formatvec = context.sc_formatvec;
 
-	err = restore_fpu_state(&context);
-
-	if (err || mangle_kernel_stack(regs, formatvec, fp))
-		goto badframe;
-
-	return 0;
+	if (restore_fpu_state(&context))
+		return -1;
 
-badframe:
-	return 1;
+	return mangle_kernel_stack(regs, formatvec, fp);
 }
 
 static inline int
@@ -697,7 +669,7 @@ rt_restore_ucontext(struct pt_regs *regs, struct switch_stack *sw,
 
 	err = __get_user(temp, &uc->uc_mcontext.version);
 	if (temp != MCONTEXT_VERSION)
-		goto badframe;
+		return -1;
 	/* restore passed registers */
 	err |= __get_user(regs->d0, &gregs[0]);
 	err |= __get_user(regs->d1, &gregs[1]);
@@ -726,24 +698,17 @@ rt_restore_ucontext(struct pt_regs *regs, struct switch_stack *sw,
 	err |= restore_altstack(&uc->uc_stack);
 
 	if (err)
-		goto badframe;
-
-	if (mangle_kernel_stack(regs, temp, &uc->uc_extra))
-		goto badframe;
+		return -1;
 
-	return 0;
-
-badframe:
-	return 1;
+	return mangle_kernel_stack(regs, temp, &uc->uc_extra);
 }
 
-asmlinkage int do_sigreturn(unsigned long __unused)
+asmlinkage void *do_sigreturn(struct pt_regs *regs, struct switch_stack *sw)
 {
-	struct switch_stack *sw = (struct switch_stack *) &__unused;
-	struct pt_regs *regs = (struct pt_regs *) (sw + 1);
 	unsigned long usp = rdusp();
 	struct sigframe __user *frame = (struct sigframe __user *)(usp - 4);
 	sigset_t set;
+	int size;
 
 	if (!access_ok(VERIFY_READ, frame, sizeof(*frame)))
 		goto badframe;
@@ -755,22 +720,22 @@ asmlinkage int do_sigreturn(unsigned long __unused)
 
 	set_current_blocked(&set);
 
-	if (restore_sigcontext(regs, &frame->sc, frame + 1))
+	size = restore_sigcontext(regs, &frame->sc, frame + 1);
+	if (size < 0)
 		goto badframe;
-	return regs->d0;
+	return (void *)sw - size;
 
 badframe:
 	force_sig(SIGSEGV, current);
-	return 0;
+	return sw;
 }
 
-asmlinkage int do_rt_sigreturn(unsigned long __unused)
+asmlinkage void *do_rt_sigreturn(struct pt_regs *regs, struct switch_stack *sw)
 {
-	struct switch_stack *sw = (struct switch_stack *) &__unused;
-	struct pt_regs *regs = (struct pt_regs *) (sw + 1);
 	unsigned long usp = rdusp();
 	struct rt_sigframe __user *frame = (struct rt_sigframe __user *)(usp - 4);
 	sigset_t set;
+	int size;
 
 	if (!access_ok(VERIFY_READ, frame, sizeof(*frame)))
 		goto badframe;
@@ -779,13 +744,14 @@ asmlinkage int do_rt_sigreturn(unsigned long __unused)
 
 	set_current_blocked(&set);
 
-	if (rt_restore_ucontext(regs, sw, &frame->uc))
+	size = rt_restore_ucontext(regs, sw, &frame->uc);
+	if (size < 0)
 		goto badframe;
-	return regs->d0;
+	return (void *)sw - size;
 
 badframe:
 	force_sig(SIGSEGV, current);
-	return 0;
+	return sw;
 }
 
 static inline struct pt_regs *rte_regs(struct pt_regs *regs)
-- 
2.17.1

[PATCH RFC 4/4] m68k equivalent of 26178ec11ef3 "x86: mm: consolidate VM_FAULT_RETRY handling" If e.g. get_user() triggers a page fault and a fatal signal is caught, we might end up with handle_mm_fault() returning VM_FAULT_RETRY and not doing anything to page tables. In such case we must *not* return to the faulting insn - that would repeat the entire thing without making any progress; what we need instead is to treat that as failed (user) memory access.

[Michael Schmitz]

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

MSch: v4.4 backport compile errors fixes.

Tested-by: Finn Thain <fthain@linux-m68k.org>
Tested-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Michael Schmitz <schmitzmic@gmail.com>
---
 arch/m68k/mm/fault.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/m68k/mm/fault.c b/arch/m68k/mm/fault.c
index 6a94cdd0c830..f94df64c3784 100644
--- a/arch/m68k/mm/fault.c
+++ b/arch/m68k/mm/fault.c
@@ -139,8 +139,11 @@ good_area:
 	fault = handle_mm_fault(mm, vma, address, flags);
 	pr_debug("handle_mm_fault returns %d\n", fault);
 
-	if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
+	if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current)) {
+		if (!user_mode(regs))
+			goto no_context;
 		return 0;
+	}
 
 	if (unlikely(fault & VM_FAULT_ERROR)) {
 		if (fault & VM_FAULT_OOM)
-- 
2.17.1

Re: [PATCH RFC 0/4]

[Michael Schmitz]

Oh dear...

$Subject ought to have read 'Some m68k v4.4 backports' (or something to 
that effect).

I'll send that series to cip-dev@lists.cip-project.org shortly if there 
are no objections.

Cheers,

     Michael

On 5/02/24 08:21, Michael Schmitz wrote:
> CIP v4.4 backport of Al Viro's misc. m68k signal handling and
> page fault fixes.
>
> The first three are a prerequisite for Finn Thain's 'm68k: Move
> signal frame following exception on 68020/030' patch, and fix
> the backport compile error seen in
> https://lore.kernel.org/oe-kbuild-all/202401310920.sBSI4BHj-lkp@intel.com/
>
> RFC version of these patches to give Geert and Al a chance to yell
> at me in case I got details of these patches wrong. I don't claim
> to understand signal handling in anywhere near the required level
> of detail.
>
> Tested on my 68030 Atari Falcon.
>
> Cheers,
>
>     Michael
>     
>

Re: [PATCH RFC 4/4] m68k equivalent of 26178ec11ef3 "x86: mm: consolidate VM_FAULT_RETRY handling" If e.g. get_user() triggers a page fault and a fatal signal is caught, we might end up with handle_mm_fault() returning VM_FAULT_RETRY and not doing anything to page tables. In such case we must *not* return to the faulting insn - that would repeat the entire thing without making any progress; what we need instead is to treat that as failed (user) memory access.

[John Paul Adrian Glaubitz]

Hi Michael,

On Mon, 2024-02-05 at 08:21 +1300, Michael Schmitz wrote:
> From: Al Viro <viro@zeniv.linux.org.uk>
> 
> MSch: v4.4 backport compile errors fixes.
> 
> Tested-by: Finn Thain <fthain@linux-m68k.org>
> Tested-by: Geert Uytterhoeven <geert@linux-m68k.org>
> Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>
> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
> Signed-off-by: Michael Schmitz <schmitzmic@gmail.com>
> ---
>  arch/m68k/mm/fault.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/m68k/mm/fault.c b/arch/m68k/mm/fault.c
> index 6a94cdd0c830..f94df64c3784 100644
> --- a/arch/m68k/mm/fault.c
> +++ b/arch/m68k/mm/fault.c
> @@ -139,8 +139,11 @@ good_area:
>  	fault = handle_mm_fault(mm, vma, address, flags);
>  	pr_debug("handle_mm_fault returns %d\n", fault);
>  
> -	if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
> +	if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current)) {
> +		if (!user_mode(regs))
> +			goto no_context;
>  		return 0;
> +	}
>  
>  	if (unlikely(fault & VM_FAULT_ERROR)) {
>  		if (fault & VM_FAULT_OOM)

That subject looks like it contains the long description which should go
into the patch instead.

Adrian

-- 
 .''`.  John Paul Adrian Glaubitz
: :' :  Debian Developer
`. `'   Physicist
  `-    GPG: 62FF 8A75 84E0 2956 9546  0006 7426 3B37 F5B5 F913

Re: [PATCH RFC 4/4] m68k equivalent of 26178ec11ef3 "x86: mm: consolidate VM_FAULT_RETRY handling" If e.g. get_user() triggers a page fault and a fatal signal is caught, we might end up with handle_mm_fault() returning VM_FAULT_RETRY and not doing anything to page tables. In such case we must *not* return to the faulting insn - that would repeat the entire thing without making any progress; what we need instead is to treat that as failed (user) memory access.

[Michael Schmitz]

Hi Adrian,

Am 05.02.2024 um 18:32 schrieb John Paul Adrian Glaubitz:
> Hi Michael,
>
> On Mon, 2024-02-05 at 08:21 +1300, Michael Schmitz wrote:
>> From: Al Viro <viro@zeniv.linux.org.uk>
>>
>> MSch: v4.4 backport compile errors fixes.
>>
>> Tested-by: Finn Thain <fthain@linux-m68k.org>
>> Tested-by: Geert Uytterhoeven <geert@linux-m68k.org>
>> Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>
>> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
>> Signed-off-by: Michael Schmitz <schmitzmic@gmail.com>
>> ---
>>  arch/m68k/mm/fault.c | 5 ++++-
>>  1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/m68k/mm/fault.c b/arch/m68k/mm/fault.c
>> index 6a94cdd0c830..f94df64c3784 100644
>> --- a/arch/m68k/mm/fault.c
>> +++ b/arch/m68k/mm/fault.c
>> @@ -139,8 +139,11 @@ good_area:
>>  	fault = handle_mm_fault(mm, vma, address, flags);
>>  	pr_debug("handle_mm_fault returns %d\n", fault);
>>
>> -	if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
>> +	if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current)) {
>> +		if (!user_mode(regs))
>> +			goto no_context;
>>  		return 0;
>> +	}
>>
>>  	if (unlikely(fault & VM_FAULT_ERROR)) {
>>  		if (fault & VM_FAULT_OOM)
>
> That subject looks like it contains the long description which should go
> into the patch instead.

Yep - I fat-fingered editing the commit message there. Thanks for spotting!

Fixed in v2.

	Michael

>
> Adrian
>