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Message-ID: <20210730142336.GA19569@C02TD0UTHF1T.local>
Date: Fri, 30 Jul 2021 15:23:36 +0100
From: Mark Rutland <mark.rutland@....com>
To: Will Deacon <will@...nel.org>
Cc: Yuchen Wei <weiyuchen3@...wei.com>, catalin.marinas@....com,
vincenzo.frascino@....com, keescook@...omium.org, pcc@...gle.com,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
He Zhe <zhe.he@...driver.com>
Subject: Re: [PATCH] arm64: audit: fix return value high 32bit truncation
problem
Hi,
[adding He Zhe]
On Fri, Jul 30, 2021 at 01:22:37PM +0100, Will Deacon wrote:
> On Thu, Jul 22, 2021 at 02:07:07PM +0800, Yuchen Wei wrote:
> > From: weiyuchen <weiyuchen3@...wei.com>
> >
> > Add error code judgment in invoke_syscall() to prevent kernel
> > components such as audit and tracepoint from obtaining incorrect
> > return values. For example:
> >
> > type=SYSCALL msg=audit(342.780:69): arch=40000028 syscall=235
> > success=yes exit=4294967235
> >
> > The syscall return value is -61, but due to the following process in
> > invoke_syscall():
> >
> > if (is_compat_task())
> > ret = lower_32_bits(ret);
> > regs->regs[0] = ret;
> >
> > The return value audit or tracepoint get from regs[0] is 4294967235,
> > which is an incorrect return value.
> >
> > Signed-off-by: weiyuchen <weiyuchen3@...wei.com>
> > ---
> > arch/arm64/kernel/syscall.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/arch/arm64/kernel/syscall.c b/arch/arm64/kernel/syscall.c
> > index 263d6c1a525f..f9f042d9a088 100644
> > --- a/arch/arm64/kernel/syscall.c
> > +++ b/arch/arm64/kernel/syscall.c
> > @@ -54,7 +54,7 @@ static void invoke_syscall(struct pt_regs *regs, unsigned int scno,
> > ret = do_ni_syscall(regs, scno);
> > }
> >
> > - if (is_compat_task())
> > + if (is_compat_task() && !IS_ERR_VALUE(ret))
> > ret = lower_32_bits(ret);
>
> Hmm, I'm worried this might break other users who don't expect to see
> non-zero bits for the upper 32-bits of a compat task.
>
> Mark -- I remember you looking into this relatively recently. Where did you
> get to with it?
Sorry, I've been meaning to chase this up for a bit.
There are a few problems here, but I think we can solve them all (patch
below).
Generally, syscall_get_return_value() should be used to get syscall
return values, and this *should* always sign-extend compat values to 64
bits (but arm64's implementation currently doesn't).
Audit currently uses regs_return_value() rather than
syscall_get_return_value(). That's mostly for historical reasons, but
some architectures don't implement syscall_get_return_value() at the
moment, so we'll have to bodge regs_return_value() on arm64 for now. On
32-bit arm regs_return_value() returns a long, and so is sign-extended.
On 32-bit arm, since syscall_get_return_value() returns a long, it'll
get sign-extended (whether returning an errno or a pointer in the high
2GiB), and we should do the same for compat. We can shuffle
syscall_get_return_value() and syscall_get_error() to handle that.
There are a few places we directly assign to the regs where we need to
truncate the assignment. We can use syscall_set_return_value() to do
that for us.
I think for now, the below should be sufficient for arm64, and we can
chase that up with some cleanup to the core audit code to use
syscall_get_return_value().
Thanks,
Mark.
---->8----
>From 20131e3e51e4b6034e11df044ae916a853be43de Mon Sep 17 00:00:00 2001
From: Mark Rutland <mark.rutland@....com>
Date: Fri, 30 Jul 2021 15:12:41 +0100
Subject: [PATCH] arm64: fix compat syscall return truncation
TODO: explain this.
Signed-off-by: Mark Rutland <mark.rutland@....com>
Cc: He Zhe <zhe.he@...driver.com>
Cc: Will Deacon <will@...nel.org>
Cc: weiyuchen <weiyuchen3@...wei.com>
---
arch/arm64/include/asm/ptrace.h | 12 +++++++++++-
arch/arm64/include/asm/syscall.h | 19 ++++++++++---------
arch/arm64/kernel/ptrace.c | 2 +-
arch/arm64/kernel/signal.c | 3 ++-
arch/arm64/kernel/syscall.c | 9 +++------
5 files changed, 27 insertions(+), 18 deletions(-)
diff --git a/arch/arm64/include/asm/ptrace.h b/arch/arm64/include/asm/ptrace.h
index e58bca832dff..41b332c054ab 100644
--- a/arch/arm64/include/asm/ptrace.h
+++ b/arch/arm64/include/asm/ptrace.h
@@ -320,7 +320,17 @@ static inline unsigned long kernel_stack_pointer(struct pt_regs *regs)
static inline unsigned long regs_return_value(struct pt_regs *regs)
{
- return regs->regs[0];
+ unsigned long val = regs->regs[0];
+
+ /*
+ * Audit currently uses regs_return_value() instead of
+ * syscall_get_return_value(). Apply the same sign-extension here until
+ * audit is updated to use syscall_get_return_value().
+ */
+ if (compat_user_mode(regs))
+ val = sign_extend64(val, 31);
+
+ return val;
}
static inline void regs_set_return_value(struct pt_regs *regs, unsigned long rc)
diff --git a/arch/arm64/include/asm/syscall.h b/arch/arm64/include/asm/syscall.h
index cfc0672013f6..03e20895453a 100644
--- a/arch/arm64/include/asm/syscall.h
+++ b/arch/arm64/include/asm/syscall.h
@@ -29,22 +29,23 @@ static inline void syscall_rollback(struct task_struct *task,
regs->regs[0] = regs->orig_x0;
}
-
-static inline long syscall_get_error(struct task_struct *task,
- struct pt_regs *regs)
+static inline long syscall_get_return_value(struct task_struct *task,
+ struct pt_regs *regs)
{
- unsigned long error = regs->regs[0];
+ unsigned long val = regs->regs[0];
if (is_compat_thread(task_thread_info(task)))
- error = sign_extend64(error, 31);
+ val = sign_extend64(val, 31);
- return IS_ERR_VALUE(error) ? error : 0;
+ return val;
}
-static inline long syscall_get_return_value(struct task_struct *task,
- struct pt_regs *regs)
+static inline long syscall_get_error(struct task_struct *task,
+ struct pt_regs *regs)
{
- return regs->regs[0];
+ unsigned long error = syscall_get_return_value(task, regs);
+
+ return IS_ERR_VALUE(error) ? error : 0;
}
static inline void syscall_set_return_value(struct task_struct *task,
diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
index 499b6b2f9757..b381a1ee9ea7 100644
--- a/arch/arm64/kernel/ptrace.c
+++ b/arch/arm64/kernel/ptrace.c
@@ -1862,7 +1862,7 @@ void syscall_trace_exit(struct pt_regs *regs)
audit_syscall_exit(regs);
if (flags & _TIF_SYSCALL_TRACEPOINT)
- trace_sys_exit(regs, regs_return_value(regs));
+ trace_sys_exit(regs, syscall_get_return_value(current, regs));
if (flags & (_TIF_SYSCALL_TRACE | _TIF_SINGLESTEP))
tracehook_report_syscall(regs, PTRACE_SYSCALL_EXIT);
diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c
index 53c2c85efb34..62e273b2d83f 100644
--- a/arch/arm64/kernel/signal.c
+++ b/arch/arm64/kernel/signal.c
@@ -29,6 +29,7 @@
#include <asm/unistd.h>
#include <asm/fpsimd.h>
#include <asm/ptrace.h>
+#include <asm/syscall.h>
#include <asm/signal32.h>
#include <asm/traps.h>
#include <asm/vdso.h>
@@ -890,7 +891,7 @@ static void do_signal(struct pt_regs *regs)
retval == -ERESTART_RESTARTBLOCK ||
(retval == -ERESTARTSYS &&
!(ksig.ka.sa.sa_flags & SA_RESTART)))) {
- regs->regs[0] = -EINTR;
+ syscall_set_return_value(current, regs, -EINTR, 0);
regs->pc = continue_addr;
}
diff --git a/arch/arm64/kernel/syscall.c b/arch/arm64/kernel/syscall.c
index 263d6c1a525f..50a0f1a38e84 100644
--- a/arch/arm64/kernel/syscall.c
+++ b/arch/arm64/kernel/syscall.c
@@ -54,10 +54,7 @@ static void invoke_syscall(struct pt_regs *regs, unsigned int scno,
ret = do_ni_syscall(regs, scno);
}
- if (is_compat_task())
- ret = lower_32_bits(ret);
-
- regs->regs[0] = ret;
+ syscall_set_return_value(current, regs, 0, ret);
/*
* Ultimately, this value will get limited by KSTACK_OFFSET_MAX(),
@@ -115,7 +112,7 @@ static void el0_svc_common(struct pt_regs *regs, int scno, int sc_nr,
* syscall. do_notify_resume() will send a signal to userspace
* before the syscall is restarted.
*/
- regs->regs[0] = -ERESTARTNOINTR;
+ syscall_set_return_value(current, regs, -ERESTARTNOINTR, 0);
return;
}
@@ -136,7 +133,7 @@ static void el0_svc_common(struct pt_regs *regs, int scno, int sc_nr,
* anyway.
*/
if (scno == NO_SYSCALL)
- regs->regs[0] = -ENOSYS;
+ syscall_set_return_value(current, regs, -ENOSYS, 0);
scno = syscall_trace_enter(regs);
if (scno == NO_SYSCALL)
goto trace_exit;
--
2.11.0
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