Messages in this thread Patch in this message | | | Date | Fri, 30 Jul 2021 15:23:36 +0100 | From | Mark Rutland <> | Subject | Re: [PATCH] arm64: audit: fix return value high 32bit truncation problem |
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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@huawei.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@huawei.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@arm.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@arm.com> Cc: He Zhe <zhe.he@windriver.com> Cc: Will Deacon <will@kernel.org> Cc: weiyuchen <weiyuchen3@huawei.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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