[PATCH 5.4 85/85] arm64: fix compat syscall return truncation

Greg Kroah-Hartman
2021-08-10T17:40:19Z

From: Mark Rutland <mark.rutland@arm.com>

commit e30e8d46cf605d216a799a28c77b8a41c328613a upstream.

Due to inconsistencies in the way we manipulate compat GPRs, we have a
few issues today:

* For audit and tracing, where error codes are handled as a (native)
long, negative error codes are expected to be sign-extended to the
native 64-bits, or they may fail to be matched correctly. Thus a
syscall which fails with an error may erroneously be identified as
failing.

* For ptrace, *all* compat return values should be sign-extended for
consistency with 32-bit arm, but we currently only do this for
negative return codes.

* As we may transiently set the upper 32 bits of some compat GPRs while
in the kernel, these can be sampled by perf, which is somewhat
confusing. This means that where a syscall returns a pointer above 2G,
this will be sign-extended, but will not be mistaken for an error as
error codes are constrained to the inclusive range [-4096, -1] where
no user pointer can exist.

To fix all of these, we must consistently use helpers to get/set the
compat GPRs, ensuring that we never write the upper 32 bits of the
return code, and always sign-extend when reading the return code. This
patch does so, with the following changes:

* We re-organise syscall_get_return_value() to always sign-extend for
compat tasks, and reimplement syscall_get_error() atop. We update
syscall_trace_exit() to use syscall_get_return_value().

* We consistently use syscall_set_return_value() to set the return
value, ensureing the upper 32 bits are never set unexpectedly.

* As the core audit code currently uses regs_return_value() rather than
syscall_get_return_value(), we special-case this for
compat_user_mode(regs) such that this will do the right thing. Going
forward, we should try to move the core audit code over to
syscall_get_return_value().

Cc: <stable@vger.kernel.org>
Reported-by: He Zhe <zhe.he@windriver.com>
Reported-by: weiyuchen <weiyuchen3@huawei.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/20210802104200.21390-1-mark.rutland@arm.com
Signed-off-by: Will Deacon <will@kernel.org>
[Mark: trivial conflict resolution for v5.4.y]
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
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 | 7 ++-----
5 files changed, 26 insertions(+), 17 deletions(-)

--- a/arch/arm64/include/asm/ptrace.h
+++ b/arch/arm64/include/asm/ptrace.h
@@ -299,7 +299,17 @@ static inline unsigned long kernel_stack

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)
--- a/arch/arm64/include/asm/syscall.h
+++ b/arch/arm64/include/asm/syscall.h
@@ -29,22 +29,23 @@ static inline void syscall_rollback(stru
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,
--- a/arch/arm64/kernel/ptrace.c
+++ b/arch/arm64/kernel/ptrace.c
@@ -1868,7 +1868,7 @@ void syscall_trace_exit(struct pt_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);
--- 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>
@@ -868,7 +869,7 @@ static void do_signal(struct pt_regs *re
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;
}

--- a/arch/arm64/kernel/syscall.c
+++ b/arch/arm64/kernel/syscall.c
@@ -50,10 +50,7 @@ static void invoke_syscall(struct pt_reg
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);
}

static inline bool has_syscall_work(unsigned long flags)
@@ -108,7 +105,7 @@ static void el0_svc_common(struct pt_reg
if (has_syscall_work(flags)) {
/* set default errno for user-issued syscall(-1) */
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;