This is a note to let you know that I've just added the patch titled
arm64: fix compat syscall return truncation
to the 5.13-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
arm64-fix-compat-syscall-return-truncation.patch
and it can be found in the queue-5.13 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From e30e8d46cf605d216a799a28c77b8a41c328613a Mon Sep 17 00:00:00 2001
From: Mark Rutland <mark.rutland@xxxxxxx>
Date: Mon, 2 Aug 2021 11:42:00 +0100
Subject: arm64: fix compat syscall return truncation
From: Mark Rutland <mark.rutland@xxxxxxx>
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@xxxxxxxxxxxxxxx>
Reported-by: He Zhe <zhe.he@xxxxxxxxxxxxx>
Reported-by: weiyuchen <weiyuchen3@xxxxxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
Reviewed-by: Catalin Marinas <catalin.marinas@xxxxxxx>
Link: https://lore.kernel.org/r/20210802104200.21390-1-mark.rutland@xxxxxxx
Signed-off-by: Will Deacon <will@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
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(-)
--- a/arch/arm64/include/asm/ptrace.h
+++ b/arch/arm64/include/asm/ptrace.h
@@ -320,7 +320,17 @@ 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
@@ -1862,7 +1862,7 @@ 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>
@@ -890,7 +891,7 @@ 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
@@ -54,10 +54,7 @@ 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);
/*
* Ultimately, this value will get limited by KSTACK_OFFSET_MAX(),
@@ -115,7 +112,7 @@ static void el0_svc_common(struct pt_reg
* 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_reg
* 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;
Patches currently in stable-queue which might be from mark.rutland@xxxxxxx are
queue-5.13/arm64-fix-compat-syscall-return-truncation.patch
queue-5.13/arm64-stacktrace-avoid-tracing-arch_stack_walk.patch
