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325cdacd03
Mike Galbraith reported a situation where a WARN_ON_ONCE() call in DRM code turned into an oops. As it turns out, WARN_ON_ONCE() seems to be completely broken when called from a module. The bug was introduced with the following commit:19d436268d("debug: Add _ONCE() logic to report_bug()") That commit changed WARN_ON_ONCE() to move its 'once' logic into the bug trap handler. It requires a writable bug table so that the BUGFLAG_DONE bit can be written to the flags to indicate the first warning has occurred. The bug table was made writable for vmlinux, which relies on vmlinux.lds.S and vmlinux.lds.h for laying out the sections. However, it wasn't made writable for modules, which rely on the ELF section header flags. Reported-by: Mike Galbraith <efault@gmx.de> Tested-by: Masami Hiramatsu <mhiramat@kernel.org> Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Fixes:19d436268d("debug: Add _ONCE() logic to report_bug()") Link: http://lkml.kernel.org/r/a53b04235a65478dd9afc51f5b329fdc65c84364.1500095401.git.jpoimboe@redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
83 lines
2.2 KiB
C
83 lines
2.2 KiB
C
#ifndef _ASM_X86_BUG_H
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#define _ASM_X86_BUG_H
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#include <linux/stringify.h>
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/*
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* Since some emulators terminate on UD2, we cannot use it for WARN.
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* Since various instruction decoders disagree on the length of UD1,
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* we cannot use it either. So use UD0 for WARN.
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*
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* (binutils knows about "ud1" but {en,de}codes it as 2 bytes, whereas
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* our kernel decoder thinks it takes a ModRM byte, which seems consistent
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* with various things like the Intel SDM instruction encoding rules)
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*/
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#define ASM_UD0 ".byte 0x0f, 0xff"
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#define ASM_UD1 ".byte 0x0f, 0xb9" /* + ModRM */
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#define ASM_UD2 ".byte 0x0f, 0x0b"
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#define INSN_UD0 0xff0f
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#define INSN_UD2 0x0b0f
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#define LEN_UD0 2
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#ifdef CONFIG_GENERIC_BUG
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#ifdef CONFIG_X86_32
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# define __BUG_REL(val) ".long " __stringify(val)
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#else
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# define __BUG_REL(val) ".long " __stringify(val) " - 2b"
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#endif
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#ifdef CONFIG_DEBUG_BUGVERBOSE
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#define _BUG_FLAGS(ins, flags) \
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do { \
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asm volatile("1:\t" ins "\n" \
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".pushsection __bug_table,\"aw\"\n" \
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"2:\t" __BUG_REL(1b) "\t# bug_entry::bug_addr\n" \
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"\t" __BUG_REL(%c0) "\t# bug_entry::file\n" \
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"\t.word %c1" "\t# bug_entry::line\n" \
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"\t.word %c2" "\t# bug_entry::flags\n" \
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"\t.org 2b+%c3\n" \
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".popsection" \
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: : "i" (__FILE__), "i" (__LINE__), \
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"i" (flags), \
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"i" (sizeof(struct bug_entry))); \
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} while (0)
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#else /* !CONFIG_DEBUG_BUGVERBOSE */
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#define _BUG_FLAGS(ins, flags) \
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do { \
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asm volatile("1:\t" ins "\n" \
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".pushsection __bug_table,\"aw\"\n" \
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"2:\t" __BUG_REL(1b) "\t# bug_entry::bug_addr\n" \
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"\t.word %c0" "\t# bug_entry::flags\n" \
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"\t.org 2b+%c1\n" \
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".popsection" \
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: : "i" (flags), \
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"i" (sizeof(struct bug_entry))); \
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} while (0)
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#endif /* CONFIG_DEBUG_BUGVERBOSE */
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#else
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#define _BUG_FLAGS(ins, flags) asm volatile(ins)
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#endif /* CONFIG_GENERIC_BUG */
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#define HAVE_ARCH_BUG
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#define BUG() \
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do { \
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_BUG_FLAGS(ASM_UD2, 0); \
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unreachable(); \
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} while (0)
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#define __WARN_FLAGS(flags) _BUG_FLAGS(ASM_UD0, BUGFLAG_WARNING|(flags))
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#include <asm-generic/bug.h>
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#endif /* _ASM_X86_BUG_H */
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