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Thu, 22 Apr 2021 09:55:47 -0700 (PDT) Date: Thu, 22 Apr 2021 17:55:45 +0100 From: Mark Rutland To: He Zhe Subject: Re: [PATCH 2/3] arm64: syscall.h: Add sign extension handling in syscall_get_return_value for compat Message-ID: <20210422165545.GE66392@C02TD0UTHF1T.local> References: <20210416075533.7720-1-zhe.he@windriver.com> <20210416075533.7720-2-zhe.he@windriver.com> <20210421174105.GB52940@C02TD0UTHF1T.local> MIME-Version: 1.0 In-Reply-To: <20210421174105.GB52940@C02TD0UTHF1T.local> X-Mimecast-Impersonation-Protect: Policy=CLT - Impersonation Protection Definition; Similar Internal Domain=false; Similar Monitored External Domain=false; Custom External Domain=false; Mimecast External Domain=false; Newly Observed Domain=false; Internal User Name=false; Custom Display Name List=false; Reply-to Address Mismatch=false; Targeted Threat Dictionary=false; Mimecast Threat Dictionary=false; Custom Threat Dictionary=false X-Scanned-By: MIMEDefang 2.78 on 10.11.54.6 X-loop: linux-audit@redhat.com X-Mailman-Approved-At: Thu, 22 Apr 2021 13:30:28 -0400 Cc: catalin.marinas@arm.com, oleg@redhat.com, linux-kernel@vger.kernel.org, linux-audit@redhat.com, will@kernel.org, linux-arm-kernel@lists.infradead.org X-BeenThere: linux-audit@redhat.com X-Mailman-Version: 2.1.12 Precedence: junk List-Id: Linux Audit Discussion List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: linux-audit-bounces@redhat.com Errors-To: linux-audit-bounces@redhat.com X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=linux-audit-bounces@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Disposition: inline Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit On Wed, Apr 21, 2021 at 06:41:05PM +0100, Mark Rutland wrote: > On Fri, Apr 16, 2021 at 03:55:32PM +0800, He Zhe wrote: > > Add sign extension handling in syscall_get_return_value so that it can > > handle 32-bit compatible case and can be used by for example audit, just > > like what syscall_get_error does. > > If a compat syscall can ever legitimately return a non-error value with > bit 31 set, and this sign-extends it, is that ever going to reach > userspace as a 64-bit value? > > IIUC things like mmap() can return pointers above 2GiB for a compat > task, so I'm a bit uneasy that we'd handle those wrong. I can't see a > way of preventing that unless we keep the upper 32 bits for errors. Looking at this with fresh eyes, I think we can more closely mirror syscall_get_error(), and do something like: static inline long syscall_get_return_value(struct task_struct *task, struct pt_regs *regs) { long val = regs->regs[0]; long error = val; if (is_compat_thread(task_thread_info(task))) error = sign_extend64(error, 31); return IS_ERR_VALUE(error) ? error : val; } Thanks, Mark. > > Mark. > > > > > Signed-off-by: He Zhe > > --- > > arch/arm64/include/asm/syscall.h | 7 ++++++- > > 1 file changed, 6 insertions(+), 1 deletion(-) > > > > diff --git a/arch/arm64/include/asm/syscall.h b/arch/arm64/include/asm/syscall.h > > index cfc0672013f6..cd7a22787aeb 100644 > > --- a/arch/arm64/include/asm/syscall.h > > +++ b/arch/arm64/include/asm/syscall.h > > @@ -44,7 +44,12 @@ static inline long syscall_get_error(struct task_struct *task, > > static inline long syscall_get_return_value(struct task_struct *task, > > struct pt_regs *regs) > > { > > - return regs->regs[0]; > > + long val = regs->regs[0]; > > + > > + if (is_compat_thread(task_thread_info(task))) > > + val = sign_extend64(val, 31); > > + > > + return val; > > } > > > > static inline void syscall_set_return_value(struct task_struct *task, > > -- > > 2.17.1 > > -- Linux-audit mailing list Linux-audit@redhat.com https://listman.redhat.com/mailman/listinfo/linux-audit