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, 38 insertions, 0 deletions

diff --git a/arch/alpha/Kconfig.debug b/arch/alpha/Kconfig.debug
new file mode 100644
index 000000000..f85f4281c
--- /dev/null
+++ b/arch/alpha/Kconfig.debug
@@ -0,0 +1,38 @@
+# SPDX-License-Identifier: GPL-2.0
+
+config EARLY_PRINTK
+	bool
+	depends on ALPHA_GENERIC || ALPHA_SRM
+	default y
+
+config ALPHA_LEGACY_START_ADDRESS
+	bool "Legacy kernel start address"
+	depends on ALPHA_GENERIC
+	default n
+	help
+	  The 2.4 kernel changed the kernel start address from 0x310000
+	  to 0x810000 to make room for the Wildfire's larger SRM console.
+	  Recent consoles on Titan and Marvel machines also require the
+	  extra room.
+
+	  If you're using aboot 0.7 or later, the bootloader will examine the
+	  ELF headers to determine where to transfer control. Unfortunately,
+	  most older bootloaders -- APB or MILO -- hardcoded the kernel start
+	  address rather than examining the ELF headers, and the result is a
+	  hard lockup.
+
+	  Say Y if you have a broken bootloader.  Say N if you do not, or if
+	  you wish to run on Wildfire, Titan, or Marvel.
+
+config ALPHA_LEGACY_START_ADDRESS
+	bool
+	depends on !ALPHA_GENERIC && !ALPHA_TITAN && !ALPHA_MARVEL && !ALPHA_WILDFIRE
+	default y
+
+config MATHEMU
+	tristate "Kernel FP software completion" if DEBUG_KERNEL && !SMP
+	default y if !DEBUG_KERNEL || SMP
+	help
+	  This option is required for IEEE compliant floating point arithmetic
+	  on the Alpha. The only time you would ever not say Y is to say M in
+	  order to debug the code. Say Y unless you know what you are doing.