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, 72 insertions, 0 deletions

diff --git a/arch/powerpc/boot/ps3-head.S b/arch/powerpc/boot/ps3-head.S
new file mode 100644
index 000000000..0a4ebfcc3
--- /dev/null
+++ b/arch/powerpc/boot/ps3-head.S
@@ -0,0 +1,72 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ *  PS3 bootwrapper entry.
+ *
+ *  Copyright (C) 2007 Sony Computer Entertainment Inc.
+ *  Copyright 2007 Sony Corp.
+ */
+
+#include "ppc_asm.h"
+
+	.machine "ppc64"
+
+	.text
+
+/*
+ * __system_reset_overlay - The PS3 first stage entry.
+ *
+ * The bootwraper build script copies the 512 bytes at symbol
+ * __system_reset_overlay to offset 0x100 of the rom image.  This symbol
+ * must occupy 512 or less bytes.
+ *
+ * The PS3 has a single processor with two threads.
+ */
+
+	.globl __system_reset_overlay
+__system_reset_overlay:
+
+	/* Switch to 32-bit mode. */
+
+	mfmsr	r9
+	clrldi	r9,r9,1
+	mtmsrd	r9
+	nop
+
+	/* Get thread number in r3 and branch. */
+
+	mfspr	r3, 0x88
+	cntlzw.	r3, r3
+	beq	1f
+
+	/* Secondary goes to __secondary_hold in kernel. */
+
+	li	r4, 0x60
+	mtctr	r4
+	bctr
+
+1:
+	/* Primary delays then goes to _zimage_start in wrapper. */
+
+	or	31, 31, 31 /* db16cyc */
+	or	31, 31, 31 /* db16cyc */
+
+	lis	r4, _zimage_start@ha
+	addi	r4, r4, _zimage_start@l
+	mtctr	r4
+	bctr
+
+	. = __system_reset_overlay + 512
+
+/*
+ * __system_reset_kernel - Place holder for the kernel reset vector.
+ *
+ * The bootwrapper build script copies 512 bytes from offset 0x100
+ * of the rom image to the symbol __system_reset_kernel.  At runtime
+ * the bootwrapper program copies the 512 bytes at __system_reset_kernel
+ * to ram address 0x100.  This symbol must occupy 512 bytes.
+ */
+
+	.globl __system_reset_kernel
+__system_reset_kernel:
+
+	. = __system_reset_kernel + 512