openrisc: fix arbitrary kernel memory access via or1k_atomic syscallgrafted

sys_or1k_atomic() (syscall 244 in the "or1k" ABI) takes two user
pointers, v1 and v2, and swaps the words they point to in hand-written
assembly.

    l.lwz   r29,0(r4)
    l.lwz   r27,0(r5)
    l.sw    0(r4),r27
    l.sw    0(r5),r29

The pointers are not checked with access_ok(). The four memory
accesses also have no exception table entries.

A caller passes a kernel address as either pointer, and the syscall
reads from and writes to it directly.

This gives an unprivileged process a kernel read/write primitive. It
overwrites kernel data such as the sys_call_table, gaining code
execution in kernel context.

Check both pointers before entering the critical section. Add fixups
for the four memory accesses so faults on valid but unmapped user
addresses return -EFAULT.

[shorne@gmail.com: fix comment style]
Fixes: 9d02a4283e9c ("OpenRISC: Boot code")
Cc: stable@vger.kernel.org
Signed-off-by: Ali Ahmet Memis <ali@iusegentoo.com>
Signed-off-by: Stafford Horne <shorne@gmail.com>

1 files changed, 96 insertions, 0 deletions

diff --git a/usr/include/headers_check.pl b/usr/include/headers_check.pl
new file mode 100755
index 000000000..6cd6eb652
--- /dev/null
+++ b/usr/include/headers_check.pl
@@ -0,0 +1,96 @@
+#!/usr/bin/env perl
+# SPDX-License-Identifier: GPL-2.0
+#
+# headers_check.pl execute a number of trivial consistency checks
+#
+# Usage: headers_check.pl dir [files...]
+# dir:   dir to look for included files
+# files: list of files to check
+#
+# The script reads the supplied files line by line and:
+#
+# 1) for each include statement it checks if the
+#    included file actually exists.
+#    Only include files located in asm* and linux* are checked.
+#    The rest are assumed to be system include files.
+#
+# 2) It is checked that prototypes does not use "extern"
+#
+# 3) Check for leaked CONFIG_ symbols
+
+use warnings;
+use strict;
+use File::Basename;
+
+my ($dir, @files) = @ARGV;
+
+my $ret = 0;
+my $line;
+my $lineno = 0;
+my $filename;
+
+foreach my $file (@files) {
+	$filename = $file;
+
+	open(my $fh, '<', $filename)
+		or die "$filename: $!\n";
+	$lineno = 0;
+	while ($line = <$fh>) {
+		$lineno++;
+		&check_include();
+		&check_asm_types();
+		&check_declarations();
+	}
+	close $fh;
+}
+exit $ret;
+
+sub check_include
+{
+	if ($line =~ m/^\s*#\s*include\s+<((asm|linux).*)>/) {
+		my $inc = $1;
+		my $found;
+		$found = stat($dir . "/" . $inc);
+		if (!$found) {
+			printf STDERR "$filename:$lineno: included file '$inc' is not exported\n";
+			$ret = 1;
+		}
+	}
+}
+
+sub check_declarations
+{
+	# soundcard.h is what it is
+	if ($line =~ m/^void seqbuf_dump\(void\);/) {
+		return;
+	}
+	# drm headers are being C++ friendly
+	if ($line =~ m/^extern "C"/) {
+		return;
+	}
+	if ($line =~ m/^(\s*extern|unsigned|char|short|int|long|void)\b/) {
+		printf STDERR "$filename:$lineno: " .
+			      "userspace cannot reference function or " .
+			      "variable defined in the kernel\n";
+		$ret = 1;
+	}
+}
+
+my $linux_asm_types;
+sub check_asm_types
+{
+	if ($filename =~ /types.h|int-l64.h|int-ll64.h/o) {
+		return;
+	}
+	if ($lineno == 1) {
+		$linux_asm_types = 0;
+	} elsif ($linux_asm_types >= 1) {
+		return;
+	}
+	if ($line =~ m/^\s*#\s*include\s+<asm\/types.h>/) {
+		$linux_asm_types = 1;
+		printf STDERR "$filename:$lineno: " .
+		"include of <linux/types.h> is preferred over <asm/types.h>\n";
+		$ret = 1;
+	}
+}