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

[Christoph Hellwig]

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 <h...@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