From: Marc Zyngier maz@kernel.org
[ Upstream commit 2a1a3fa0f29270583f0e6e3100d609e09697add1 ]
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: ffc5089196446 ("[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 Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/kallsyms.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c index 127e7cfafa552..3e1b66366ac23 100644 --- a/kernel/kallsyms.c +++ b/kernel/kallsyms.c @@ -296,8 +296,10 @@ 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); }