kernel.git/arch/x86/include/asm/bug.h, branch linux-5.18.y

x86/bug: Prevent shadowing in __WARN_FLAGS

2022-04-05T08:24:40Z

The macro __WARN_FLAGS() uses a local variable named "f". This being a common name, there is a risk of shadowing other variables. For example, GCC would yield: | In file included from ./include/linux/bug.h:5, | from ./include/linux/cpumask.h:14, | from ./arch/x86/include/asm/cpumask.h:5, | from ./arch/x86/include/asm/msr.h:11, | from ./arch/x86/include/asm/processor.h:22, | from ./arch/x86/include/asm/timex.h:5, | from ./include/linux/timex.h:65, | from ./include/linux/time32.h:13, | from ./include/linux/time.h:60, | from ./include/linux/stat.h:19, | from ./include/linux/module.h:13, | from virt/lib/irqbypass.mod.c:1: | ./include/linux/rcupdate.h: In function 'rcu_head_after_call_rcu': | ./arch/x86/include/asm/bug.h:80:21: warning: declaration of 'f' shadows a parameter [-Wshadow] | 80 | __auto_type f = BUGFLAG_WARNING|(flags); \ | | ^ | ./include/asm-generic/bug.h:106:17: note: in expansion of macro '__WARN_FLAGS' | 106 | __WARN_FLAGS(BUGFLAG_ONCE | \ | | ^~~~~~~~~~~~ | ./include/linux/rcupdate.h:1007:9: note: in expansion of macro 'WARN_ON_ONCE' | 1007 | WARN_ON_ONCE(func != (rcu_callback_t)~0L); | | ^~~~~~~~~~~~ | In file included from ./include/linux/rbtree.h:24, | from ./include/linux/mm_types.h:11, | from ./include/linux/buildid.h:5, | from ./include/linux/module.h:14, | from virt/lib/irqbypass.mod.c:1: | ./include/linux/rcupdate.h:1001:62: note: shadowed declaration is here | 1001 | rcu_head_after_call_rcu(struct rcu_head *rhp, rcu_callback_t f) | | ~~~~~~~~~~~~~~~^ For reference, sparse also warns about it, c.f. [1]. This patch renames the variable from f to __flags (with two underscore prefixes as suggested in the Linux kernel coding style [2]) in order to prevent collisions. [1] https://lore.kernel.org/all/CAFGhKbyifH1a+nAMCvWM88TK6fpNPdzFtUXPmRGnnQeePV+1sw@mail.gmail.com/ [2] Linux kernel coding style, section 12) Macros, Enums and RTL, paragraph 5) namespace collisions when defining local variables in macros resembling functions https://www.kernel.org/doc/html/latest/process/coding-style.html#macros-enums-and-rtl Fixes: bfb1a7c91fb7 ("x86/bug: Merge annotate_reachable() into_BUG_FLAGS() asm") Signed-off-by: Vincent Mailhol Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Nick Desaulniers Acked-by: Josh Poimboeuf Link: https://lkml.kernel.org/r/20220324023742.106546-1-mailhol.vincent@wanadoo.fr

x86,objtool: Move the ASM_REACHABLE annotation to objtool.h

2022-03-15T09:32:45Z

Because we need a variant for .S files too. Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/Yi9gOW9f1GGwwUD6@hirez.programming.kicks-ass.net

x86/bug: Merge annotate_reachable() into _BUG_FLAGS() asm

2022-02-02T22:41:04Z

In __WARN_FLAGS(), we had two asm statements (abbreviated): asm volatile("ud2"); asm volatile(".pushsection .discard.reachable"); These pair of statements are used to trigger an exception, but then help objtool understand that for warnings, control flow will be restored immediately afterwards. The problem is that volatile is not a compiler barrier. GCC explicitly documents this: > Note that the compiler can move even volatile asm instructions > relative to other code, including across jump instructions. Also, no clobbers are specified to prevent instructions from subsequent statements from being scheduled by compiler before the second asm statement. This can lead to instructions from subsequent statements being emitted by the compiler before the second asm statement. Providing a scheduling model such as via -march= options enables the compiler to better schedule instructions with known latencies to hide latencies from data hazards compared to inline asm statements in which latencies are not estimated. If an instruction gets scheduled by the compiler between the two asm statements, then objtool will think that it is not reachable, producing a warning. To prevent instructions from being scheduled in between the two asm statements, merge them. Also remove an unnecessary unreachable() asm annotation from BUG() in favor of __builtin_unreachable(). objtool is able to track that the ud2 from BUG() terminates control flow within the function. Link: https://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html#Volatile Link: https://github.com/ClangBuiltLinux/linux/issues/1483 Signed-off-by: Nick Desaulniers Signed-off-by: Josh Poimboeuf Link: https://lore.kernel.org/r/20220202205557.2260694-1-ndesaulniers@google.com

x86: Delete UD0, UD1 traces

2021-05-05T19:50:13Z

Both instructions aren't used by kernel. Signed-off-by: Alexey Dobriyan Signed-off-by: Thomas Gleixner Link: https://lore.kernel.org/r/YIHHYNKbiSf5N7+o@localhost.localdomain

compiler.h: Move instrumentation_begin()/end() to new header

2020-07-24T11:56:23Z

Linus pointed out that compiler.h - which is a key header that gets included in every single one of the 28,000+ kernel files during a kernel build - was bloated in: 655389666643: ("vmlinux.lds.h: Create section for protection against instrumentation") Linus noted: > I have pulled this, but do we really want to add this to a header file > that is _so_ core that it gets included for basically every single > file built? > > I don't even see those instrumentation_begin/end() things used > anywhere right now. > > It seems excessive. That 53 lines is maybe not a lot, but it pushed > that header file to over 12kB, and while it's mostly comments, it's > extra IO and parsing basically for _every_ single file compiled in the > kernel. > > For what appears to be absolutely zero upside right now, and I really > don't see why this should be in such a core header file! Move these primitives into a new header: , and include that header in the headers that make use of it. Unfortunately one of these headers is asm-generic/bug.h, which does get included in a lot of places, similarly to compiler.h. So the de-bloating effect isn't as good as we'd like it to be - but at least the interfaces are defined separately. No change to functionality intended. Reported-by: Linus Torvalds Signed-off-by: Ingo Molnar Link: https://lore.kernel.org/r/20200604071921.GA1361070@gmail.com Cc: Thomas Gleixner Cc: Borislav Petkov Cc: Peter Zijlstra

x86/entry, bug: Comment the instrumentation_begin() usage for WARN()

2020-06-15T12:10:10Z

Explain the rationale for annotating WARN(), even though, strictly speaking printk() and friends are very much not safe in many of the places we put them. Signed-off-by: Peter Zijlstra (Intel)

bug: Annotate WARN/BUG/stackfail as noinstr safe

2020-06-11T13:14:36Z

Warnings, bugs and stack protection fails from noinstr sections, e.g. low level and early entry code, are likely to be fatal. Mark them as "safe" to be invoked from noinstr protected code to avoid annotating all usage sites. Getting the information out is important. Signed-off-by: Thomas Gleixner Reviewed-by: Alexandre Chartre Acked-by: Peter Zijlstra Link: https://lkml.kernel.org/r/20200505134100.376598577@linutronix.de

x86: bug.h: use asm_inline in _BUG_FLAGS definitions

2019-09-15T18:14:15Z

This helps preventing a BUG* or WARN* in some static inline from preventing that (or one of its callers) being inlined, so should allow gcc to make better informed inlining decisions. For example, with gcc 9.2, tcp_fastopen_no_cookie() vanishes from net/ipv4/tcp_fastopen.o. It does not itself have any BUG or WARN, but it calls dst_metric() which has a WARN_ON_ONCE - and despite that WARN_ON_ONCE vanishing since the condition is compile-time false, dst_metric() is apparently sufficiently "large" that when it gets inlined into tcp_fastopen_no_cookie(), the latter becomes too large for inlining. Overall, if one asks size(1), .text decreases a little and .data increases by about the same amount (x86-64 defconfig) $ size vmlinux.{before,after} text data bss dec hex filename 19709726 5202600 1630280 26542606 195020e vmlinux.before 19709330 5203068 1630280 26542678 1950256 vmlinux.after while bloat-o-meter says add/remove: 10/28 grow/shrink: 103/51 up/down: 3669/-2854 (815) ... Total: Before=14783683, After=14784498, chg +0.01% Acked-by: Ingo Molnar Signed-off-by: Rasmus Villemoes Signed-off-by: Miguel Ojeda

Revert "x86/bug: Macrofy the BUG table section handling, to work around GCC inlining bugs"

2018-12-19T11:00:00Z

This reverts commit f81f8ad56fd1c7b99b2ed1c314527f7d9ac447c6. See this commit for details about the revert: e769742d3584 ("Revert "x86/jump-labels: Macrofy inline assembly code to work around GCC inlining bugs"") Reported-by: Masahiro Yamada Reviewed-by: Borislav Petkov Reviewed-by: Thomas Gleixner Cc: Juergen Gross Cc: Richard Biener Cc: Kees Cook Cc: Segher Boessenkool Cc: Ard Biesheuvel Cc: Peter Zijlstra Cc: Josh Poimboeuf Cc: Nadav Amit Cc: Linus Torvalds Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar

x86/bug: Macrofy the BUG table section handling, to work around GCC inlining bugs

2018-10-04T09:25:00Z

As described in: 77b0bf55bc67: ("kbuild/Makefile: Prepare for using macros in inline assembly code to work around asm() related GCC inlining bugs") GCC's inlining heuristics are broken with common asm() patterns used in kernel code, resulting in the effective disabling of inlining. The workaround is to set an assembly macro and call it from the inline assembly block. As a result GCC considers the inline assembly block as a single instruction. (Which it isn't, but that's the best we can get.) This patch increases the kernel size: text data bss dec hex filename 18146889 10225380 2957312 31329581 1de0d2d ./vmlinux before 18147336 10226688 2957312 31331336 1de1408 ./vmlinux after (+1755) But enables more aggressive inlining (and probably better branch decisions). The number of static text symbols in vmlinux is much lower: Before: 40218 After: 40053 (-165) The assembly code gets harder to read due to the extra macro layer. [ mingo: Rewrote the changelog. ] Tested-by: Kees Cook Signed-off-by: Nadav Amit Acked-by: Peter Zijlstra (Intel) Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Brian Gerst Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Josh Poimboeuf Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/20181003213100.189959-7-namit@vmware.com Signed-off-by: Ingo Molnar