Subject: [PATCH 2/3] arm64: signal: sigreturn() and rt_sigreturn() sometime returns the wrong signals

From: Liam Howlett <[email-masked]>
Date: Tue, 20 Apr 2021 16:50:13 +0000

arm64_notify_segfault() was used to force a SIGSEGV in all error cases
in sigreturn() and rt_sigreturn() to avoid writing a new sig handler.
There is now a better sig handler to use which does not search the VMA
address space and return a slightly incorrect error code.  Restore the
older and correct si_code of SI_KERNEL by using arm64_notify_die().  In
the case of !access_ok(), simply return SIGSEGV with si_code
SEGV_ACCERR.

This change requires exporting arm64_notfiy_die() to the arm64 traps.h

Fixes: f71016a8a8c5 (arm64: signal: Call arm64_notify_segfault when
failing to deliver signal)
Signed-off-by: Liam R. Howlett <[email-masked]>
---
 arch/arm64/include/asm/traps.h |  2 ++
 arch/arm64/kernel/signal.c     |  8 ++++++--
 arch/arm64/kernel/signal32.c   | 18 ++++++++++++++----
 3 files changed, 22 insertions(+), 6 deletions(-)

diff --git a/arch/arm64/include/asm/traps.h b/arch/arm64/include/asm/traps.h
index 54f32a0675df..9b76144fcba6 100644
--- a/arch/arm64/include/asm/traps.h
+++ b/arch/arm64/include/asm/traps.h
@@ -29,6 +29,8 @@ void arm64_notify_segfault(unsigned long addr);
 void arm64_force_sig_fault(int signo, int code, unsigned long far, const char *str);
 void arm64_force_sig_mceerr(int code, unsigned long far, short lsb, const char *str);
 void arm64_force_sig_ptrace_errno_trap(int errno, unsigned long far, const char *str);
+void arm64_notify_die(const char *str, struct pt_regs *regs, int signo,
+		      int sicode, unsigned long far, int err);
 
 /*
  * Move regs->pc to next instruction and do necessary setup before it
diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c
index 6237486ff6bb..9fde6dc760c3 100644
--- a/arch/arm64/kernel/signal.c
+++ b/arch/arm64/kernel/signal.c
@@ -544,7 +544,7 @@ SYSCALL_DEFINE0(rt_sigreturn)
 	frame = (struct rt_sigframe __user *)regs->sp;
 
 	if (!access_ok(frame, sizeof (*frame)))
-		goto badframe;
+		goto e_access;
 
 	if (restore_sigframe(regs, frame))
 		goto badframe;
@@ -555,7 +555,11 @@ SYSCALL_DEFINE0(rt_sigreturn)
 	return regs->regs[0];
 
 badframe:
-	arm64_notify_segfault(regs->sp);
+	arm64_notify_die("Bad frame", regs, SIGSEGV, SI_KERNEL, regs->sp, 0);
+	return 0;
+
+e_access:
+	force_signal_inject(SIGSEGV, SEGV_ACCERR, regs->sp, 0);
 	return 0;
 }
 
diff --git a/arch/arm64/kernel/signal32.c b/arch/arm64/kernel/signal32.c
index 2f507f565c48..af8b6c0eb8aa 100644
--- a/arch/arm64/kernel/signal32.c
+++ b/arch/arm64/kernel/signal32.c
@@ -248,7 +248,7 @@ COMPAT_SYSCALL_DEFINE0(sigreturn)
 	frame = (struct compat_sigframe __user *)regs->compat_sp;
 
 	if (!access_ok(frame, sizeof (*frame)))
-		goto badframe;
+		goto e_access;
 
 	if (compat_restore_sigframe(regs, frame))
 		goto badframe;
@@ -256,7 +256,12 @@ COMPAT_SYSCALL_DEFINE0(sigreturn)
 	return regs->regs[0];
 
 badframe:
-	arm64_notify_segfault(regs->compat_sp);
+	arm64_notify_die("Bad frame", regs, SIGSEGV, SI_KERNEL,
+			 regs->compat_sp, 0);
+	return 0;
+
+e_access:
+	force_signal_inject(SIGSEGV, SEGV_ACCERR, regs->compat_sp, 0);
 	return 0;
 }
 
@@ -279,7 +284,7 @@ COMPAT_SYSCALL_DEFINE0(rt_sigreturn)
 	frame = (struct compat_rt_sigframe __user *)regs->compat_sp;
 
 	if (!access_ok(frame, sizeof (*frame)))
-		goto badframe;
+		goto e_access;
 
 	if (compat_restore_sigframe(regs, &frame->sig))
 		goto badframe;
@@ -290,7 +295,12 @@ COMPAT_SYSCALL_DEFINE0(rt_sigreturn)
 	return regs->regs[0];
 
 badframe:
-	arm64_notify_segfault(regs->compat_sp);
+	arm64_notify_die("Bad frame", regs, SIGSEGV, SI_KERNEL,
+			 regs->compat_sp, 0);
+	return 0;
+
+e_access:
+	force_signal_inject(SIGSEGV, SEGV_ACCERR, regs->compat_sp, 0);
 	return 0;
 }
 
-- 
2.30.2