linux-kernel - [PATCH 5.1 52/85] signal/arm64: Use force_sig not force_sig

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Date:   Fri,  7 Jun 2019 17:39:37 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Dave Martin <Dave.Martin@....com>,
        James Morse <james.morse@....com>,
        Will Deacon <will.deacon@....com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>
Subject: [PATCH 5.1 52/85] signal/arm64: Use force_sig not force_sig_fault for SIGKILL

From: Eric W. Biederman <ebiederm@...ssion.com>

commit d76cac67db40c172791ce07948367b96a758e45b upstream.

I don't think this is userspace visible but SIGKILL does not have
any si_codes that use the fault member of the siginfo union.  Correct
this the simple way and call force_sig instead of force_sig_fault when
the signal is SIGKILL.

The two know places where synchronous SIGKILL are generated are
do_bad_area and fpsimd_save.  The call paths to force_sig_fault are:
do_bad_area
  arm64_force_sig_fault
    force_sig_fault
force_signal_inject
  arm64_notify_die
    arm64_force_sig_fault
       force_sig_fault

Which means correcting this in arm64_force_sig_fault is enough
to ensure the arm64 code is not misusing the generic code, which
could lead to maintenance problems later.

Cc: stable@...r.kernel.org
Cc: Dave Martin <Dave.Martin@....com>
Cc: James Morse <james.morse@....com>
Cc: Will Deacon <will.deacon@....com>
Fixes: af40ff687bc9 ("arm64: signal: Ensure si_code is valid for all fault signals")
Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
Signed-off-by: Will Deacon <will.deacon@....com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/arm64/kernel/traps.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

--- a/arch/arm64/kernel/traps.c
+++ b/arch/arm64/kernel/traps.c
@@ -256,7 +256,10 @@ void arm64_force_sig_fault(int signo, in
 			   const char *str)
 {
 	arm64_show_signal(signo, str);
-	force_sig_fault(signo, code, addr, current);
+	if (signo == SIGKILL)
+		force_sig(SIGKILL, current);
+	else
+		force_sig_fault(signo, code, addr, current);
 }

 void arm64_force_sig_mceerr(int code, void __user *addr, short lsb,