From aecfd220b223043475fa515aa563249f683fcd04 Mon Sep 17 00:00:00 2001 From: Kees Cook Date: Wed, 3 Jun 2020 13:28:45 -0700 Subject: x86/mm/numa: Remove uninitialized_var() usage Using uninitialized_var() is dangerous as it papers over real bugs[1] (or can in the future), and suppresses unrelated compiler warnings (e.g. "unused variable"). If the compiler thinks it is uninitialized, either simply initialize the variable or make compiler changes. As a precursor to removing[2] this[3] macro[4], refactor code to avoid its need. The original reason for its use here was to work around the #ifdef being the only place the variable was used. This is better expressed using IS_ENABLED() and a new code block where the variable can be used unconditionally. [1] https://lore.kernel.org/lkml/20200603174714.192027-1-glider@google.com/ [2] https://lore.kernel.org/lkml/CA+55aFw+Vbj0i=1TGqCR5vQkCzWJ0QxK6CernOU6eedsudAixw@mail.gmail.com/ [3] https://lore.kernel.org/lkml/CA+55aFwgbgqhbp1fkxvRKEpzyR5J8n1vKT1VZdz9knmPuXhOeg@mail.gmail.com/ [4] https://lore.kernel.org/lkml/CA+55aFz2500WfbKXAx8s67wrm9=yVJu65TpLgN_ybYNv0VEOKA@mail.gmail.com/ Fixes: 1e01979c8f50 ("x86, numa: Implement pfn -> nid mapping granularity check") Signed-off-by: Kees Cook --- include/linux/page-flags-layout.h | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) (limited to 'include/linux') diff --git a/include/linux/page-flags-layout.h b/include/linux/page-flags-layout.h index 71283739ffd2..e200eef6a7fd 100644 --- a/include/linux/page-flags-layout.h +++ b/include/linux/page-flags-layout.h @@ -98,9 +98,11 @@ /* * We are going to use the flags for the page to node mapping if its in * there. This includes the case where there is no node, so it is implicit. + * Note that this #define MUST have a value so that it can be tested with + * the IS_ENABLED() macro. */ #if !(NODES_WIDTH > 0 || NODES_SHIFT == 0) -#define NODE_NOT_IN_PAGE_FLAGS +#define NODE_NOT_IN_PAGE_FLAGS 1 #endif #if defined(CONFIG_NUMA_BALANCING) && LAST_CPUPID_WIDTH == 0 -- cgit v1.2.3 From 63a0895d960aa3d3653ef0ecad5bd8579388f14b Mon Sep 17 00:00:00 2001 From: Kees Cook Date: Wed, 3 Jun 2020 13:09:38 -0700 Subject: compiler: Remove uninitialized_var() macro Using uninitialized_var() is dangerous as it papers over real bugs[1] (or can in the future), and suppresses unrelated compiler warnings (e.g. "unused variable"). If the compiler thinks it is uninitialized, either simply initialize the variable or make compiler changes. As recommended[2] by[3] Linus[4], remove the macro. With the recent change to disable -Wmaybe-uninitialized in v5.7 in commit 78a5255ffb6a ("Stop the ad-hoc games with -Wno-maybe-initialized"), this is likely the best time to make this treewide change. [1] https://lore.kernel.org/lkml/20200603174714.192027-1-glider@google.com/ [2] https://lore.kernel.org/lkml/CA+55aFw+Vbj0i=1TGqCR5vQkCzWJ0QxK6CernOU6eedsudAixw@mail.gmail.com/ [3] https://lore.kernel.org/lkml/CA+55aFwgbgqhbp1fkxvRKEpzyR5J8n1vKT1VZdz9knmPuXhOeg@mail.gmail.com/ [4] https://lore.kernel.org/lkml/CA+55aFz2500WfbKXAx8s67wrm9=yVJu65TpLgN_ybYNv0VEOKA@mail.gmail.com/ Suggested-by: Linus Torvalds Reviewed-by: Bart van Assche Reviewed-by: Miguel Ojeda Tested-by: Nathan Chancellor Tested-by: Sedat Dilek Signed-off-by: Kees Cook --- include/linux/compiler-clang.h | 2 -- include/linux/compiler-gcc.h | 6 ------ 2 files changed, 8 deletions(-) (limited to 'include/linux') diff --git a/include/linux/compiler-clang.h b/include/linux/compiler-clang.h index 5e55302e3bf6..8a072d00e688 100644 --- a/include/linux/compiler-clang.h +++ b/include/linux/compiler-clang.h @@ -5,8 +5,6 @@ /* Compiler specific definitions for Clang compiler */ -#define uninitialized_var(x) x = *(&(x)) - /* same as gcc, this was present in clang-2.6 so we can assume it works * with any version that can compile the kernel */ diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h index 1c74464c80c6..4099ac8b7f10 100644 --- a/include/linux/compiler-gcc.h +++ b/include/linux/compiler-gcc.h @@ -59,12 +59,6 @@ (typeof(ptr)) (__ptr + (off)); \ }) -/* - * A trick to suppress uninitialized variable warning without generating any - * code - */ -#define uninitialized_var(x) x = x - #ifdef CONFIG_RETPOLINE #define __noretpoline __attribute__((__indirect_branch__("keep"))) #endif -- cgit v1.2.3