From: Dmitry V. Levin ldv@altlinux.org
commit b3583fca5fb654af2cfc1c08259abb9728272538 upstream.
If both the tracer and the tracee are compat processes, and gprs[2] is assigned a value by __poke_user_compat, then the higher 32 bits of gprs[2] are cleared, IS_ERR_VALUE() always returns false, and syscall_get_error() always returns 0.
Fix the implementation by sign-extending the value for compat processes the same way as x86 implementation does.
The bug was exposed to user space by commit 201766a20e30f ("ptrace: add PTRACE_GET_SYSCALL_INFO request") and detected by strace test suite.
This change fixes strace syscall tampering on s390.
Link: https://lkml.kernel.org/r/20200602180051.GA2427@altlinux.org Fixes: 753c4dd6a2fa2 ("[S390] ptrace changes") Cc: Elvira Khabirova lineprinter@altlinux.org Cc: stable@vger.kernel.org # v2.6.28+ Signed-off-by: Dmitry V. Levin ldv@altlinux.org Signed-off-by: Heiko Carstens heiko.carstens@de.ibm.com Signed-off-by: Vasily Gorbik gor@linux.ibm.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
diff --git a/arch/s390/include/asm/syscall.h b/arch/s390/include/asm/syscall.h index f073292e9fdb..d9d5de0f67ff 100644 --- a/arch/s390/include/asm/syscall.h +++ b/arch/s390/include/asm/syscall.h @@ -33,7 +33,17 @@ static inline void syscall_rollback(struct task_struct *task, static inline long syscall_get_error(struct task_struct *task, struct pt_regs *regs) { - return IS_ERR_VALUE(regs->gprs[2]) ? regs->gprs[2] : 0; + unsigned long error = regs->gprs[2]; +#ifdef CONFIG_COMPAT + if (test_tsk_thread_flag(task, TIF_31BIT)) { + /* + * Sign-extend the value so (int)-EFOO becomes (long)-EFOO + * and will match correctly in comparisons. + */ + error = (long)(int)error; + } +#endif + return IS_ERR_VALUE(error) ? error : 0; }
static inline long syscall_get_return_value(struct task_struct *task,