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kallsyms: Don't let kallsyms_lookup_size_offset() fail on retrieving the first symbol

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An arm64 kernel configured with

  CONFIG_KPROBES=y
  CONFIG_KALLSYMS=y
  # CONFIG_KALLSYMS_ALL is not set
  CONFIG_KALLSYMS_BASE_RELATIVE=y

reports the following kprobe failure:

  [    0.032677] kprobes: failed to populate blacklist: -22
  [    0.033376] Please take care of using kprobes.

It appears that kprobe fails to retrieve the symbol at address
0xffff000010081000, despite this symbol being in System.map:

  ffff000010081000 T __exception_text_start

This symbol is part of the first group of aliases in the
kallsyms_offsets array (symbol names generated using ugly hacks in
scripts/kallsyms.c):

  kallsyms_offsets:
          .long   0x1000 // do_undefinstr
          .long   0x1000 // efi_header_end
          .long   0x1000 // _stext
          .long   0x1000 // __exception_text_start
          .long   0x12b0 // do_cp15instr

Looking at the implementation of get_symbol_pos(), it returns the
lowest index for aliasing symbols. In this case, it return 0.

But kallsyms_lookup_size_offset() considers 0 as a failure, which
is obviously wrong (there is definitely a valid symbol living there).
In turn, the kprobe blacklisting stops abruptly, hence the original
error.

A CONFIG_KALLSYMS_ALL kernel wouldn't fail as there is always
some random symbols at the beginning of this array, which are never
looked up via kallsyms_lookup_size_offset.

Fix it by considering that get_symbol_pos() is always successful
(which is consistent with the other uses of this function).

Fixes: ffc5089196 ("[PATCH] Create kallsyms_lookup_size_offset()")
Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Will Deacon <will@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Will Deacon <will@kernel.org>
This commit is contained in:
Marc Zyngier 2019-08-24 14:12:31 +01:00 committed by Will Deacon
parent b6143d10d2
commit 2a1a3fa0f2
1 changed files with 4 additions and 2 deletions
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6
kernel/kallsyms.c
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@ -263,8 +263,10 @@ int kallsyms_lookup_size_offset(unsigned long addr, unsigned long *symbolsize,
{
char namebuf[KSYM_NAME_LEN];
if (is_ksym_addr(addr))
return !!get_symbol_pos(addr, symbolsize, offset);
if (is_ksym_addr(addr)) {
get_symbol_pos(addr, symbolsize, offset);
return 1;
}
return !!module_address_lookup(addr, symbolsize, offset, NULL, namebuf) ||
!!__bpf_address_lookup(addr, symbolsize, offset, namebuf);
}