| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <57D0203E.1070901@linaro.org>
Date: Wed, 7 Sep 2016 10:12:14 -0400
From: David Long <dave.long@...aro.org>
To: Masami Hiramatsu <mhiramat@...nel.org>
Cc: Ananth N Mavinakayanahalli <ananth@...ux.vnet.ibm.com>,
Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
"David S. Miller" <davem@...emloft.net>,
Will Deacon <will.deacon@....com>,
linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
catalin.marinas@....com,
Sandeepa Prabhu <sandeepa.s.prabhu@...il.com>,
William Cohen <wcohen@...hat.com>,
Pratyush Anand <panand@...hat.com>,
Mark Brown <broonie@...nel.org>
Subject: Re: [PATCH v2] arm64: Improve kprobes test for atomic sequence
On 09/07/2016 01:52 AM, Masami Hiramatsu wrote:
> On Tue, 6 Sep 2016 13:54:59 -0400
> David Long <dave.long@...aro.org> wrote:
>
>> From: "David A. Long" <dave.long@...aro.org>
>>
>> Kprobes searches backwards a finite number of instructions to determine if
>> there is an attempt to probe a load/store exclusive sequence. It stops when
>> it hits the maximum number of instructions or a load or store exclusive.
>> However this means it can run up past the beginning of the function and
>> start looking at literal constants. This has been shown to cause a false
>> positive and blocks insertion of the probe. To fix this, further limit the
>> backwards search to stop if it hits a symbol address from kallsyms. The
>> presumption is that this is the entry point to this code (particularly for
>> the common case of placing probes at the beginning of functions).
>>
>> This also improves efficiency by not searching code that is not part of the
>> function. There may be some possibility that the label might not denote the
>> entry path to the probed instruction but the likelihood seems low and this
>> is just another example of how the kprobes user really needs to be
>> careful about what they are doing.
>
> Hi Dave,
>
> kallsyms_lookup_size_offset() part looks good to me. By the way,
> is there any reason we'll check the _text and module's base address
> boundary?
> I think those are already searced by kallsyms_lookup_size_offset(),
> so you don't need to check those. If the address is not found by
> kallsyms_lookup_size_offset(), that address maybe out-of-text.
>
CONFIG KPROBES does currently select CONFIG_KALLSYMS, but is it wise for
this code to depend on that? Perhaps the text boundary checking should
be moved under an else clause for the case of
kallsyms_lookup_size_offset() failing?
> Thank you,
>>
>> Signed-off-by: David A. Long <dave.long@...aro.org>
>> ---
>> arch/arm64/kernel/probes/decode-insn.c | 48 +++++++++++++++++++++++-----------
>> 1 file changed, 33 insertions(+), 15 deletions(-)
>>
>> diff --git a/arch/arm64/kernel/probes/decode-insn.c b/arch/arm64/kernel/probes/decode-insn.c
>> index 37e47a9..356ee52 100644
>> --- a/arch/arm64/kernel/probes/decode-insn.c
>> +++ b/arch/arm64/kernel/probes/decode-insn.c
>> @@ -16,6 +16,7 @@
>> #include <linux/kernel.h>
>> #include <linux/kprobes.h>
>> #include <linux/module.h>
>> +#include <linux/kallsyms.h>
>> #include <asm/kprobes.h>
>> #include <asm/insn.h>
>> #include <asm/sections.h>
>> @@ -122,7 +123,7 @@ arm_probe_decode_insn(kprobe_opcode_t insn, struct arch_specific_insn *asi)
>> static bool __kprobes
>> is_probed_address_atomic(kprobe_opcode_t *scan_start, kprobe_opcode_t *scan_end)
>> {
>> - while (scan_start > scan_end) {
>> + while (scan_start >= scan_end) {
>> /*
>> * atomic region starts from exclusive load and ends with
>> * exclusive store.
>> @@ -144,26 +145,43 @@ arm_kprobe_decode_insn(kprobe_opcode_t *addr, struct arch_specific_insn *asi)
>> kprobe_opcode_t insn = le32_to_cpu(*addr);
>> kprobe_opcode_t *scan_start = addr - 1;
>> kprobe_opcode_t *scan_end = addr - MAX_ATOMIC_CONTEXT_SIZE;
>> + unsigned long size = 0, offset = 0;
>> #if defined(CONFIG_MODULES) && defined(MODULES_VADDR)
>> struct module *mod;
>> #endif
>>
>> - if (addr >= (kprobe_opcode_t *)_text &&
>> - scan_end < (kprobe_opcode_t *)_text)
>> - scan_end = (kprobe_opcode_t *)_text;
>> + /*
>> + * If there's a symbol defined in front of and near enough to
>> + * the probe address assume it is the entry point to this
>> + * code and use it to further limit how far back we search
>> + * when determining if we're in an atomic sequence.
>> + */
>> + if (kallsyms_lookup_size_offset((unsigned long) addr, &size, &offset))
>> + if (offset < (MAX_ATOMIC_CONTEXT_SIZE*sizeof(kprobe_opcode_t)))
>> + scan_end = addr - (offset / sizeof(kprobe_opcode_t));
>> +
>> + if (scan_end <= scan_start) {
>> + if (addr >= (kprobe_opcode_t *)_text &&
>> + scan_end < (kprobe_opcode_t *)_text)
>> + scan_end = (kprobe_opcode_t *)_text;
>> #if defined(CONFIG_MODULES) && defined(MODULES_VADDR)
>> - else {
>> - preempt_disable();
>> - mod = __module_address((unsigned long)addr);
>> - if (mod && within_module_init((unsigned long)addr, mod) &&
>> - !within_module_init((unsigned long)scan_end, mod))
>> - scan_end = (kprobe_opcode_t *)mod->init_layout.base;
>> - else if (mod && within_module_core((unsigned long)addr, mod) &&
>> - !within_module_core((unsigned long)scan_end, mod))
>> - scan_end = (kprobe_opcode_t *)mod->core_layout.base;
>> - preempt_enable();
>> - }
>> + else {
>> + preempt_disable();
>> + mod = __module_address((unsigned long)addr);
>> + if (mod &&
>> + within_module_init((unsigned long)addr, mod) &&
>> + !within_module_init((unsigned long)scan_end, mod))
>> + scan_end =
>> + (kprobe_opcode_t *)mod->init_layout.base;
>> + else if (mod &&
>> + within_module_core((unsigned long)addr, mod) &&
>> + !within_module_core((unsigned long)scan_end, mod))
>> + scan_end =
>> + (kprobe_opcode_t *)mod->core_layout.base;
>> + preempt_enable();
>> + }
>> #endif
>> + }
>> decoded = arm_probe_decode_insn(insn, asi);
>>
>> if (decoded == INSN_REJECTED ||
>> --
>> 2.5.0
>>
Thanks,
-dl
Powered by blists - more mailing lists