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Date: Tue, 9 Oct 2018 13:20:13 +0200 From: Rasmus Villemoes <linux@...musvillemoes.dk> To: Jason Baron <jbaron@...mai.com>, Andrew Morton <akpm@...ux-foundation.org> Cc: linux-kernel@...r.kernel.org, Rasmus Villemoes <linux@...musvillemoes.dk> Subject: [PATCH v2 23/23] x86: dynamic_debug: protect against dynamic debug identifier reuse Most invocations of DEFINE_DYNAMIC_DEBUG_METADATA happen through "public" macros such as pr_debug or netdev_dbg, which have been updated to ensure they pass a unique identifier to use as the name for the struct _ddebug instance. But it is still possible that someone invokes DEFINE_DYNAMIC_DEBUG_METADATA directly, or creates a new wrapper macro that does not do the extra-level-of-macros-passing-on-a__UNIQUE_ID dance. On x86-64, all subsequent uses of that same identifier would silently reuse the first instance, which is bad. But we can catch such cases by defining a guard symbol that is unique per expansion of DEFINE_DYNAMIC_DEBUG_METADATA. This still allows gcc to emit multiple copies of some static inline function that has a pr_debug call (because all such copies would pass the same value of %5 to the assembler), but prevents repeated naked DEFINE_DYNAMIC_DEBUG_METADATA(descriptor, "bla") - even with a helpful error message saying that '"descriptor" used as _ddebug identifer more than once'. Acked-by: Jason Baron <jbaron@...mai.com> Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk> --- arch/x86/include/asm/dynamic_debug.h | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/arch/x86/include/asm/dynamic_debug.h b/arch/x86/include/asm/dynamic_debug.h index 350ef6e2feff..69167f40482c 100644 --- a/arch/x86/include/asm/dynamic_debug.h +++ b/arch/x86/include/asm/dynamic_debug.h @@ -26,10 +26,15 @@ "\t.long 0 \t# <padding>\n" \ _DPRINTK_ASM_KEY_INIT \ ".popsection\n" \ + ".set "__stringify(name)".ddebug.once, %c5\n" \ + ".elseif "__stringify(name)".ddebug.once - %c5\n" \ + ".line "__stringify(__LINE__) " - 1\n" \ + ".error \"'"__stringify(name)"' used as _ddebug identifier more than once\"\n" \ ".endif\n" \ : : "i" (KBUILD_MODNAME), "i" (__func__), \ "i" (__FILE__), "i" (fmt), \ - "i" (_DPRINTK_FLAGS_LINENO_INIT)) + "i" (_DPRINTK_FLAGS_LINENO_INIT), \ + "i" (__COUNTER__)) #endif /* _ASM_X86_DYNAMIC_DEBUG_H */ -- 2.19.1.3.g1d92a00e68
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