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Subject[PATCH] arm: Blacklist gcc 4.8.[012] and 4.9.0 with CONFIG_FRAME_POINTER
Date
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@iki.fi>
Reported-by: Felipe Balbi <balbi@ti.com>
Cc: Rabin Vincent <rabin@rab.in>
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
---
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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