[PATCH] arm: Blacklist gcc 4.8.[012] and 4.9.0 with CONFIG_FRAME_POINTER

[Peter Hurley]

gcc versions 4.8.[012] and 4.9.0 generates code that prematurely
adjusts the stack pointer such that still-to-be-referenced locals
are below the stack pointer, which allows them to be overwritten
by interrupts.

On 10/09/2014 04:41 PM, Rabin Vincent wrote:
>   4.8.1 and 4.8.2 are known to miscompile the ARM kernel and these
>   find_get_entry() crashes with 0xffffffff involved smell a lot like the
>   earlier reports from kernels build with those compilers:
>
>   https://lkml.org/lkml/2014/6/25/456
>   https://lkml.org/lkml/2014/6/30/375
>   https://lkml.org/lkml/2014/6/30/660
>   https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58854
>   https://lkml.org/lkml/2014/5/9/330
>
> Also, I didn't see any public email making a definitive link between GCC
> PR 58854 that Nathan pointed out in https://lkml.org/lkml/2014/6/30/660
> and the earlier find_get_entry() crashes, but I just built GCC 4.8.1 and
> an ARM kernel with that, and the GCC bug is clearly seen in
> radix_tree_lookup_slot() which returns the pointer which
> find_get_entry() is dereferencing:
>
>   <radix_tree_lookup_slot>:
>    e1a0c00d  mov     ip, sp
>    e92dd800  push    {fp, ip, lr, pc}
>    e24cb004  sub     fp, ip, #4
>    e24dd008  sub     sp, sp, #8
>    e3a02000  mov     r2, #0
>    e24b3010  sub     r3, fp, #16
>    ebffffc5  bl      c0176ab8 <__radix_tree_lookup>
>    e24bd00c  sub     sp, fp, #12		<--- sp moved up
>    e3500000  cmp     r0, #0
>    151b0010  ldrne   r0, [fp, #-16]		<--- load from under sp
>    e89da800  ldm     sp, {fp, sp, pc}
>

See gcc PR 58854, https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58854

Reported-by: Aaro Koskinen <aaro.koskinen@xxxxxx>
Reported-by: Felipe Balbi <balbi@xxxxxx>
Cc: Rabin Vincent <rabin@xxxxxx>
Signed-off-by: Peter Hurley <peter@xxxxxxxxxxxxxxxxxx>
---
 include/linux/compiler-gcc4.h | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/include/linux/compiler-gcc4.h b/include/linux/compiler-gcc4.h
index 2507fd2..4069fb2 100644
--- a/include/linux/compiler-gcc4.h
+++ b/include/linux/compiler-gcc4.h
@@ -86,3 +86,17 @@
 #define __HAVE_BUILTIN_BSWAP16__
 #endif
 #endif /* CONFIG_ARCH_USE_BUILTIN_BSWAP */
+
+/*
+ * For ARCH=arm, gcc versions 4.8.[012] and 4.9.0 generate code that closes
+ * the stack frame prematurely which allows still-in-use locals to be
+ * overwritten by interrupts
+ *
+ * see PR 58854, https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58854
+ */
+#ifdef __KERNEL__
+# if ((GCC_VERSION >= 40800 && GCC_VERSION <= 40802) || GCC_VERSION == 40900) \
+	&& defined(__arm__) && defined(CONFIG_FRAME_POINTER)
+#  error Your version of gcc miscompiles stack frames
+# endif
+#endif
-- 
2.1.1

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