Commit e30e8d46 authored by Mark Rutland's avatar Mark Rutland Committed by Will Deacon

arm64: fix compat syscall return truncation

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: default avatarHe Zhe <zhe.he@windriver.com>
Reported-by: default avatarweiyuchen <weiyuchen3@huawei.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Reviewed-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/20210802104200.21390-1-mark.rutland@arm.comSigned-off-by: default avatarWill Deacon <will@kernel.org>
parent d8a71905
......@@ -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)
......
......@@ -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,
......
......@@ -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);
......
......@@ -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;
}
......
......@@ -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;
......
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