From: He Zhe <zhe.he@windriver.com>
To: Will Deacon <will@kernel.org>, Mark Rutland <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
oleg@redhat.com, linux-kernel@vger.kernel.org,
linux-audit@redhat.com, linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 1/3] arm64: ptrace: Add is_syscall_success to handle compat
Date: Tue, 20 Apr 2021 16:54:22 +0800 [thread overview]
Message-ID: <1e13b428-1dbd-55ff-ed2f-5ac7f6562689@windriver.com> (raw)
In-Reply-To: <20210419121932.GA30004@willie-the-truck>
On 4/19/21 8:19 PM, Will Deacon wrote:
> On Fri, Apr 16, 2021 at 02:34:41PM +0100, Mark Rutland wrote:
>> On Fri, Apr 16, 2021 at 01:33:22PM +0100, Catalin Marinas wrote:
>>> On Fri, Apr 16, 2021 at 03:55:31PM +0800, He Zhe wrote:
>>>> The general version of is_syscall_success does not handle 32-bit
>>>> compatible case, which would cause 32-bit negative return code to be
>>>> recoganized as a positive number later and seen as a "success".
>>>>
>>>> Since is_compat_thread is defined in compat.h, implementing
>>>> is_syscall_success in ptrace.h would introduce build failure due to
>>>> recursive inclusion of some basic headers like mutex.h. We put the
>>>> implementation to ptrace.c
>>>>
>>>> Signed-off-by: He Zhe <zhe.he@windriver.com>
>>>> ---
>>>> arch/arm64/include/asm/ptrace.h | 3 +++
>>>> arch/arm64/kernel/ptrace.c | 10 ++++++++++
>>>> 2 files changed, 13 insertions(+)
>>>>
>>>> diff --git a/arch/arm64/include/asm/ptrace.h b/arch/arm64/include/asm/ptrace.h
>>>> index e58bca832dff..3c415e9e5d85 100644
>>>> --- a/arch/arm64/include/asm/ptrace.h
>>>> +++ b/arch/arm64/include/asm/ptrace.h
>>>> @@ -328,6 +328,9 @@ static inline void regs_set_return_value(struct pt_regs *regs, unsigned long rc)
>>>> regs->regs[0] = rc;
>>>> }
>>>>
>>>> +extern inline int is_syscall_success(struct pt_regs *regs);
>>>> +#define is_syscall_success(regs) is_syscall_success(regs)
>>>> +
>>>> /**
>>>> * regs_get_kernel_argument() - get Nth function argument in kernel
>>>> * @regs: pt_regs of that context
>>>> diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
>>>> index 170f42fd6101..3266201f8c60 100644
>>>> --- a/arch/arm64/kernel/ptrace.c
>>>> +++ b/arch/arm64/kernel/ptrace.c
>>>> @@ -1909,3 +1909,13 @@ int valid_user_regs(struct user_pt_regs *regs, struct task_struct *task)
>>>> else
>>>> return valid_native_regs(regs);
>>>> }
>>>> +
>>>> +inline int is_syscall_success(struct pt_regs *regs)
>>>> +{
>>>> + unsigned long val = regs->regs[0];
>>>> +
>>>> + if (is_compat_thread(task_thread_info(current)))
>>>> + val = sign_extend64(val, 31);
>>>> +
>>>> + return !IS_ERR_VALUE(val);
>>>> +}
>>> It's better to use compat_user_mode(regs) here instead of
>>> is_compat_thread(). It saves us from worrying whether regs are for the
>>> current context.
>>>
>>> I think we should change regs_return_value() instead. This function
>>> seems to be called from several other places and it has the same
>>> potential problems if called on compat pt_regs.
>> I think this is a problem we created for ourselves back in commit:
>>
>> 15956689a0e60aa0 ("arm64: compat: Ensure upper 32 bits of x0 are zero on syscall return)
>>
>> AFAICT, the perf regs samples are the only place this matters, since for
>> ptrace the compat regs are implicitly truncated to compat_ulong_t, and
>> audit expects the non-truncated return value. Other architectures don't
>> truncate here, so I think we're setting ourselves up for a game of
>> whack-a-mole to truncate and extend wherever we need to.
>>
>> Given that, I suspect it'd be better to do something like the below.
>>
>> Will, thoughts?
> I think perf is one example, but this is also visible to userspace via the
> native ptrace interface and I distinctly remember needing this for some
> versions of arm64 strace to work correctly when tracing compat tasks.
>
> So I do think that clearing the upper bits on the return path is the right
> approach, but it sounds like we need some more work to handle syscall(-1)
> and audit (what exactly is the problem here after these patches have been
> applied?)
IIUC, IS_ERR_VALUE could handle -1, did I miss something? Thanks.
Regards,
Zhe
>
> Will
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next prev parent reply other threads:[~2021-04-20 11:58 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-16 7:55 [PATCH 1/3] arm64: ptrace: Add is_syscall_success to handle compat He Zhe
2021-04-16 7:55 ` [PATCH 2/3] arm64: syscall.h: Add sign extension handling in syscall_get_return_value for compat He Zhe
2021-04-16 9:43 ` Oleg Nesterov
2021-04-20 8:38 ` He Zhe
2021-04-21 17:41 ` Mark Rutland
2021-04-22 16:55 ` Mark Rutland
2021-04-16 7:55 ` [PATCH 3/3] audit: Use syscall_get_return_value to get syscall return code in audit_syscall_exit He Zhe
2021-04-16 12:33 ` [PATCH 1/3] arm64: ptrace: Add is_syscall_success to handle compat Catalin Marinas
2021-04-16 13:34 ` Mark Rutland
2021-04-17 13:19 ` David Laight
2021-04-19 12:19 ` Will Deacon
2021-04-20 8:54 ` He Zhe [this message]
2021-04-21 17:10 ` Mark Rutland
2021-04-22 16:07 ` Will Deacon
2021-04-22 16:42 ` Mark Rutland
2021-04-22 18:57 ` Dmitry V. Levin
2021-04-20 8:42 ` He Zhe
2021-04-21 17:17 ` Mark Rutland
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