[PATCH 1/9] kernel: add a PF_FORCE_COMPAT flag

Christoph Hellwig
2020-09-18T12:45:57Z

Add a flag to force processing a syscall as a compat syscall. This is
required so that in_compat_syscall() works for I/O submitted by io_uring
helper threads on behalf of compat syscalls.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
arch/sparc/include/asm/compat.h | 3 ++-
arch/x86/include/asm/compat.h | 2 +-
fs/io_uring.c | 9 +++++++++
include/linux/compat.h | 5 ++++-
include/linux/sched.h | 1 +
5 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/arch/sparc/include/asm/compat.h b/arch/sparc/include/asm/compat.h
index 40a267b3bd5208..fee6c51d36e869 100644
--- a/arch/sparc/include/asm/compat.h
+++ b/arch/sparc/include/asm/compat.h
@@ -211,7 +211,8 @@ static inline int is_compat_task(void)
static inline bool in_compat_syscall(void)
{
/* Vector 0x110 is LINUX_32BIT_SYSCALL_TRAP */
- return pt_regs_trap_type(current_pt_regs()) == 0x110;
+ return pt_regs_trap_type(current_pt_regs()) == 0x110 ||
+ (current->flags & PF_FORCE_COMPAT);
}
#define in_compat_syscall in_compat_syscall
#endif
diff --git a/arch/x86/include/asm/compat.h b/arch/x86/include/asm/compat.h
index d4edf281fff49d..fbab072d4e5b31 100644
--- a/arch/x86/include/asm/compat.h
+++ b/arch/x86/include/asm/compat.h
@@ -208,7 +208,7 @@ static inline bool in_32bit_syscall(void)
#ifdef CONFIG_COMPAT
static inline bool in_compat_syscall(void)
{
- return in_32bit_syscall();
+ return in_32bit_syscall() || (current->flags & PF_FORCE_COMPAT);
}
#define in_compat_syscall in_compat_syscall /* override the generic impl */
#endif
diff --git a/fs/io_uring.c b/fs/io_uring.c
index 3790c7fe9fee22..5755d557c3f7bc 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -5449,6 +5449,9 @@ static int io_req_defer_prep(struct io_kiocb *req,
if (unlikely(ret))
return ret;

+ if (req->ctx->compat)
+ current->flags |= PF_FORCE_COMPAT;
+
switch (req->opcode) {
case IORING_OP_NOP:
break;
@@ -5546,6 +5549,7 @@ static int io_req_defer_prep(struct io_kiocb *req,
break;
}

+ current->flags &= ~PF_FORCE_COMPAT;
return ret;
}

@@ -5669,6 +5673,9 @@ static int io_issue_sqe(struct io_kiocb *req, const struct io_uring_sqe *sqe,
struct io_ring_ctx *ctx = req->ctx;
int ret;

+ if (ctx->compat)
+ current->flags |= PF_FORCE_COMPAT;
+
switch (req->opcode) {
case IORING_OP_NOP:
ret = io_nop(req, cs);
@@ -5898,6 +5905,8 @@ static int io_issue_sqe(struct io_kiocb *req, const struct io_uring_sqe *sqe,
break;
}

+ current->flags &= ~PF_FORCE_COMPAT;
+
if (ret)
return ret;

diff --git a/include/linux/compat.h b/include/linux/compat.h
index b354ce58966e2d..685066f7ad325f 100644
--- a/include/linux/compat.h
+++ b/include/linux/compat.h
@@ -891,7 +891,10 @@ asmlinkage long compat_sys_socketcall(int call, u32 __user *args);
*/

#ifndef in_compat_syscall
-static inline bool in_compat_syscall(void) { return is_compat_task(); }
+static inline bool in_compat_syscall(void)
+{
+ return is_compat_task() || (current->flags & PF_FORCE_COMPAT);
+}
#endif

/**
diff --git a/include/linux/sched.h b/include/linux/sched.h
index afe01e232935fa..c8b183b5655a1e 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1491,6 +1491,7 @@ extern struct pid *cad_pid;
*/
#define PF_IDLE 0x00000002 /* I am an IDLE thread */
#define PF_EXITING 0x00000004 /* Getting shut down */
+#define PF_FORCE_COMPAT 0x00000008 /* acting as compat task */
#define PF_VCPU 0x00000010 /* I'm a virtual CPU */
#define PF_WQ_WORKER 0x00000020 /* I'm a workqueue worker */
#define PF_FORKNOEXEC 0x00000040 /* Forked but didn't exec */
--
2.28.0