Re: [PATCH 3/5] mips: sanitize restart logics

David Daney <ddaney@xxxxxxxxxxxxxxxxxx> · Wed, 29 Sep 2010 11:28:08 -0700

On 09/28/2010 10:50 AM, Al Viro wrote:

Put the original syscall number into ->regs[0] when we leave syscall
with error.  Use it in restart logics.  Everything else will have
it 0 since we pass through SAVE_SOME on all the ways in.  Note that
in places like bad_stack and inllegal_syscall we leave it 0 - it's
not restartable.


IIRC Userspace getcontext/setcontext rely on regs[0] having a value of 
zero in the when the signal handlers are invoked.

I haven't fully traced through the code, but I hope that this 
'invariant' holds both before and after this patch.  I think Maciej did 
the work on getcontext/setcontext, he may know for sure what the 
requirements are.

David Daney


Signed-off-by: Al Viro<viro@xxxxxxxxxxxxxxxxxx>
---
  arch/mips/kernel/branch.c      |    1 -
  arch/mips/kernel/scall32-o32.S |    9 ++++-----
  arch/mips/kernel/scall64-64.S  |    7 ++++---
  arch/mips/kernel/scall64-n32.S |    6 ++++--
  arch/mips/kernel/scall64-o32.S |    7 ++++---
  arch/mips/kernel/signal.c      |   37 ++++++++++++++++++-------------------
  arch/mips/kernel/unaligned.c   |    2 --
  7 files changed, 34 insertions(+), 35 deletions(-)

diff --git a/arch/mips/kernel/branch.c b/arch/mips/kernel/branch.c
index 0176ed0..32103cc 100644
--- a/arch/mips/kernel/branch.c
+++ b/arch/mips/kernel/branch.c
@@ -40,7 +40,6 @@ int __compute_return_epc(struct pt_regs *regs)
  		return -EFAULT;
  	}

-	regs->regs[0] = 0;
  	switch (insn.i_format.opcode) {
  	/*
  	 * jr and jalr are in r_format format.
diff --git a/arch/mips/kernel/scall32-o32.S b/arch/mips/kernel/scall32-o32.S
index 17202bb..d3edb9f 100644
--- a/arch/mips/kernel/scall32-o32.S
+++ b/arch/mips/kernel/scall32-o32.S
@@ -63,9 +63,9 @@ stack_done:
  	sw	t0, PT_R7(sp)		# set error flag
  	beqz	t0, 1f

+	lw	t1, PR_R2(sp)		# syscall number
  	negu	v0			# error
-	sw	v0, PT_R0(sp)		# set flag for syscall
-					# restarting
+	sw	t1, PT_R0(sp)		# save it for syscall restarting
  1:	sw	v0, PT_R2(sp)		# result

  o32_syscall_exit:
@@ -104,9 +104,9 @@ syscall_trace_entry:
  	sw	t0, PT_R7(sp)		# set error flag
  	beqz	t0, 1f

+	lw	t1, PT_R2(sp)		# syscall number
  	negu	v0			# error
-	sw	v0, PT_R0(sp)		# set flag for syscall
-					# restarting
+	sw	t1, PT_R0(sp)		# save it for syscall restarting
  1:	sw	v0, PT_R2(sp)		# result

  	j	syscall_exit
@@ -170,7 +170,6 @@ stackargs:
  	 */
  bad_stack:
  	negu	v0				# error
-	sw	v0, PT_R0(sp)
  	sw	v0, PT_R2(sp)
  	li	t0, 1				# set error flag
  	sw	t0, PT_R7(sp)
diff --git a/arch/mips/kernel/scall64-64.S b/arch/mips/kernel/scall64-64.S
index a8a6c59..eb0bb73 100644
--- a/arch/mips/kernel/scall64-64.S
+++ b/arch/mips/kernel/scall64-64.S
@@ -66,9 +66,9 @@ NESTED(handle_sys64, PT_SIZE, sp)
  	sd	t0, PT_R7(sp)		# set error flag
  	beqz	t0, 1f

+	ld	t1, PT_R2(sp)		# syscall number
  	dnegu	v0			# error
-	sd	v0, PT_R0(sp)		# set flag for syscall
-					# restarting
+	sd	t1, PT_R0(sp)		# save it for syscall restarting
  1:	sd	v0, PT_R2(sp)		# result

  n64_syscall_exit:
@@ -109,8 +109,9 @@ syscall_trace_entry:
  	sd	t0, PT_R7(sp)		# set error flag
  	beqz	t0, 1f

+	ld	t1, PT_R2(sp)		# syscall number
  	dnegu	v0			# error
-	sd	v0, PT_R0(sp)		# set flag for syscall restarting
+	sd	t1, PT_R0(sp)		# save it for syscall restarting
  1:	sd	v0, PT_R2(sp)		# result

  	j	syscall_exit
diff --git a/arch/mips/kernel/scall64-n32.S b/arch/mips/kernel/scall64-n32.S
index a3d6613..4da3faf 100644
--- a/arch/mips/kernel/scall64-n32.S
+++ b/arch/mips/kernel/scall64-n32.S
@@ -65,8 +65,9 @@ NESTED(handle_sysn32, PT_SIZE, sp)
  	sd	t0, PT_R7(sp)		# set error flag
  	beqz	t0, 1f

+	ld	t1, PT_R2(sp)		# syscall number
  	dnegu	v0			# error
-	sd	v0, PT_R0(sp)		# set flag for syscall restarting
+	sd	t1, PT_R0(sp)		# save it for syscall restarting
  1:	sd	v0, PT_R2(sp)		# result

  	local_irq_disable		# make sure need_resched and
@@ -106,8 +107,9 @@ n32_syscall_trace_entry:
  	sd	t0, PT_R7(sp)		# set error flag
  	beqz	t0, 1f

+	ld	t1, PT_R2(sp)		# syscall number
  	dnegu	v0			# error
-	sd	v0, PT_R0(sp)		# set flag for syscall restarting
+	sd	t1, PT_R0(sp)		# save it for syscall restarting
  1:	sd	v0, PT_R2(sp)		# result

  	j	syscall_exit
diff --git a/arch/mips/kernel/scall64-o32.S b/arch/mips/kernel/scall64-o32.S
index 813689e..7ce0a36 100644
--- a/arch/mips/kernel/scall64-o32.S
+++ b/arch/mips/kernel/scall64-o32.S
@@ -93,8 +93,9 @@ NESTED(handle_sys, PT_SIZE, sp)
  	sd	t0, PT_R7(sp)		# set error flag
  	beqz	t0, 1f

+	ld	t1, PT_R2(sp)		# syscall number
  	dnegu	v0			# error
-	sd	v0, PT_R0(sp)		# flag for syscall restarting
+	sd	t1, PT_R0(sp)		# save it for syscall restarting
  1:	sd	v0, PT_R2(sp)		# result

  o32_syscall_exit:
@@ -142,8 +143,9 @@ trace_a_syscall:
  	sd	t0, PT_R7(sp)		# set error flag
  	beqz	t0, 1f

+	ld	t1, PT_R2(sp)		# syscall number
  	dnegu	v0			# error
-	sd	v0, PT_R0(sp)		# set flag for syscall restarting
+	sd	t1, PT_R0(sp)		# save it for syscall restarting
  1:	sd	v0, PT_R2(sp)		# result

  	j	syscall_exit
@@ -155,7 +157,6 @@ trace_a_syscall:
  	 */
  bad_stack:
  	dnegu	v0			# error
-	sd	v0, PT_R0(sp)
  	sd	v0, PT_R2(sp)
  	li	t0, 1			# set error flag
  	sd	t0, PT_R7(sp)
diff --git a/arch/mips/kernel/signal.c b/arch/mips/kernel/signal.c
index b3273ae..604f077 100644
--- a/arch/mips/kernel/signal.c
+++ b/arch/mips/kernel/signal.c
@@ -550,23 +550,26 @@ static int handle_signal(unsigned long sig, siginfo_t *info,
  	struct mips_abi *abi = current->thread.abi;
  	void *vdso = current->mm->context.vdso;

-	switch(regs->regs[0]) {
-	case ERESTART_RESTARTBLOCK:
-	case ERESTARTNOHAND:
-		regs->regs[2] = EINTR;
-		break;
-	case ERESTARTSYS:
-		if (!(ka->sa.sa_flags&  SA_RESTART)) {
+	if (regs->regs[0]) {
+		switch(regs->regs[2]) {
+		case ERESTART_RESTARTBLOCK:
+		case ERESTARTNOHAND:
  			regs->regs[2] = EINTR;
  			break;
+		case ERESTARTSYS:
+			if (!(ka->sa.sa_flags&  SA_RESTART)) {
+				regs->regs[2] = EINTR;
+				break;
+			}
+		/* fallthrough */
+		case ERESTARTNOINTR:
+			regs->regs[7] = regs->regs[26];
+			regs->regs[2] = regs->regs[0];
+			regs->cp0_epc -= 4;
  		}
-	/* fallthrough */
-	case ERESTARTNOINTR:		/* Userland will reload $v0.  */
-		regs->regs[7] = regs->regs[26];
-		regs->cp0_epc -= 8;
-	}

-	regs->regs[0] = 0;		/* Don't deal with this again.  */
+		regs->regs[0] = 0;		/* Don't deal with this again.  */
+	}

  	if (sig_uses_siginfo(ka))
  		ret = abi->setup_rt_frame(vdso + abi->rt_signal_return_offset,
@@ -625,17 +628,13 @@ static void do_signal(struct pt_regs *regs)
  		return;
  	}

-	/*
-	 * Who's code doesn't conform to the restartable syscall convention
-	 * dies here!!!  The li instruction, a single machine instruction,
-	 * must directly be followed by the syscall instruction.
-	 */
  	if (regs->regs[0]) {
  		if (regs->regs[2] == ERESTARTNOHAND ||
  		    regs->regs[2] == ERESTARTSYS ||
  		    regs->regs[2] == ERESTARTNOINTR) {
+			regs->regs[2] = regs->regs[0];
  			regs->regs[7] = regs->regs[26];
-			regs->cp0_epc -= 8;
+			regs->cp0_epc -= 4;
  		}
  		if (regs->regs[2] == ERESTART_RESTARTBLOCK) {
  			regs->regs[2] = current->thread.abi->restart;
diff --git a/arch/mips/kernel/unaligned.c b/arch/mips/kernel/unaligned.c
index 69b039c..33d5a5c 100644
--- a/arch/mips/kernel/unaligned.c
+++ b/arch/mips/kernel/unaligned.c
@@ -109,8 +109,6 @@ static void emulate_load_store_insn(struct pt_regs *regs,
  	unsigned long value;
  	unsigned int res;

-	regs->regs[0] = 0;
-
  	/*
  	 * This load never faults.
  	 */

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