Merge tag 'trace-v7.3-2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-tracegrafted

Pull tracing fixes from Steven Rostedt:

 - Fix error output of boot instance creation failure

   Currently if a boot instance creation fails, instead of printing out
   the name of the instance that failed, it prints "(null)". That is
   because it prints "cur_str" that had already been processed by
   strsep(). Print the saved name instead.

   While at it, print the error code of the failure.

 - Fix use-after-free for same named historgrams

   Histograms can be named so that they can be used in multiple events.
   But if the named histogram has a variable attached, the second event
   that uses the named histogram which duplicates it and needs to free
   the original after duplication leaves the old variable in place and
   still visible. If another histogram uses than variable, it will use
   the stale one which will try to reference the freed duplicate
   histogram and crash the kernel.

   Free the duplicate variables along with the duplicated histogram
   data.

 - Check return value of kthread_run() in event self test

   The events self tests uses a kthread for testing but does not check
   if it succeeded in creating a kthread. If the kthread creation were
   to fail, the code will still try to call kthread_stop() on the error
   returned.

 - Fix race between reading trace_pipe and updating subbuffer size

   If a user is reading the trace_pipe file at the same time they update
   the ring buffer sub-buffer size, can cause the trace_pipe read to
   read stale data. Add trace_access_lock() around updating the ring
   buffer sub-buffer size.

 - Fix eventfs_inode on failure path in creation of the events directory

   In the creation of the "events" directory, if after allocating the
   eventfs_inode a failure is detected, it calls cleanup_ei() which
   calls free_ei(). The free_ei() will test if eventfs_inode being freed
   has no children. It is a bug if it does. But on the failure case of
   the creation of the "events" directory, the children lists have not
   yet been initialized and the free will trigger a warning because
   list_empty() on an uninitialized list returns false.

   Move the initialization into init_ei() where it makes more sense and
   makes sure that a created eventfs_inode has its lists initialized
   upon creation.

 - Check return value of kthread_run() in ftrace direct sample code

   The sample code that shows how to use the ftrace direct calls does
   not test the return of kthread_run() to see if it succeeds. Return a
   failure if the kthread_run() doesn't succeed.

 - Clear user events state on fork in case of alloc failure

   On fork, the child gets a pointer to the parent's user events state.
   It makes a copy of it then updates the child's pointer to it. But if
   the allocation fails, the duplication function leaves the child with
   a pointer to its parent's descriptor. When the child cleans up its
   data, it will free the parent's descriptor while the parent is still
   using it.

   In the duplication function, set the child's user_event_mm to NULL
   before testing if the allocation succeeded, and when it exits it will
   not free the parent's descriptor.

 - Fix retry exhaustion in simple ring buffer reader swap

   simple_ring_buffer_swap_reader_page() starts with retry set to 8 and
   post-decrements it only after a failed link replacement. On the final
   attempt, a successful replacement leaves retry at zero, while a
   failed replacement leaves it at -1.

   But the check for success expects the retry value to be non-zero and
   exits with an error on zero. This is the opposite result. Fix it.

 - Fail nicely when the remote swap_reader_page() returns an error

   Currently, if the swap_reader_page() of a remote buffer fails, it
   triggers a WARN_ON_ONCE() and continues normally. Instead, have it
   exit with an error and a pr_warn() print instead of a full WARNING.

* tag 'trace-v7.3-2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace:
  ring-buffer: Stop remote reader update when page swap fails
  tracing: Fix retry exhaustion in simple ring buffer reader swap
  tracing/user_events: Clear copied tracing state before fork duplication
  samples/ftrace: Fix kthread_stop() on ERR_PTR in ftrace-direct-multi-modify
  samples/ftrace: Fix kthread_stop() on ERR_PTR in ftrace-direct-modify
  eventfs: Initialize ei->children and ei->list in init_ei()
  tracing: Fix use-after-free in trace_pipe read on sub-buffer order change
  tracing: Fix crash passing ERR_PTR to kthread_stop()
  tracing: Fix use-after-free with same-name named triggers
  tracing: Fix logged instance name on creation failure

1 files changed, 305 insertions, 0 deletions

diff --git a/arch/mips/math-emu/dsemul.c b/arch/mips/math-emu/dsemul.c
new file mode 100644
index 000000000..e02bd20b6
--- /dev/null
+++ b/arch/mips/math-emu/dsemul.c
@@ -0,0 +1,305 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/err.h>
+#include <linux/slab.h>
+#include <linux/mm_types.h>
+#include <linux/sched/task.h>
+
+#include <asm/branch.h>
+#include <asm/cacheflush.h>
+#include <asm/fpu_emulator.h>
+#include <asm/inst.h>
+#include <asm/mipsregs.h>
+#include <linux/uaccess.h>
+
+/**
+ * struct emuframe - The 'emulation' frame structure
+ * @emul:	The instruction to 'emulate'.
+ * @badinst:	A break instruction to cause a return to the kernel.
+ *
+ * This structure defines the frames placed within the delay slot emulation
+ * page in response to a call to mips_dsemul(). Each thread may be allocated
+ * only one frame at any given time. The kernel stores within it the
+ * instruction to be 'emulated' followed by a break instruction, then
+ * executes the frame in user mode. The break causes a trap to the kernel
+ * which leads to do_dsemulret() being called unless the instruction in
+ * @emul causes a trap itself, is a branch, or a signal is delivered to
+ * the thread. In these cases the allocated frame will either be reused by
+ * a subsequent delay slot 'emulation', or be freed during signal delivery or
+ * upon thread exit.
+ *
+ * This approach is used because:
+ *
+ * - Actually emulating all instructions isn't feasible. We would need to
+ *   be able to handle instructions from all revisions of the MIPS ISA,
+ *   all ASEs & all vendor instruction set extensions. This would be a
+ *   whole lot of work & continual maintenance burden as new instructions
+ *   are introduced, and in the case of some vendor extensions may not
+ *   even be possible. Thus we need to take the approach of actually
+ *   executing the instruction.
+ *
+ * - We must execute the instruction within user context. If we were to
+ *   execute the instruction in kernel mode then it would have access to
+ *   kernel resources without very careful checks, leaving us with a
+ *   high potential for security or stability issues to arise.
+ *
+ * - We used to place the frame on the users stack, but this requires
+ *   that the stack be executable. This is bad for security so the
+ *   per-process page is now used instead.
+ *
+ * - The instruction in @emul may be something entirely invalid for a
+ *   delay slot. The user may (intentionally or otherwise) place a branch
+ *   in a delay slot, or a kernel mode instruction, or something else
+ *   which generates an exception. Thus we can't rely upon the break in
+ *   @badinst always being hit. For this reason we track the index of the
+ *   frame allocated to each thread, allowing us to clean it up at later
+ *   points such as signal delivery or thread exit.
+ *
+ * - The user may generate a fake struct emuframe if they wish, invoking
+ *   the BRK_MEMU break instruction themselves. We must therefore not
+ *   trust that BRK_MEMU means there's actually a valid frame allocated
+ *   to the thread, and must not allow the user to do anything they
+ *   couldn't already.
+ */
+struct emuframe {
+	mips_instruction	emul;
+	mips_instruction	badinst;
+};
+
+static const int emupage_frame_count = PAGE_SIZE / sizeof(struct emuframe);
+
+static inline __user struct emuframe *dsemul_page(void)
+{
+	return (__user struct emuframe *)STACK_TOP;
+}
+
+static int alloc_emuframe(void)
+{
+	mm_context_t *mm_ctx = &current->mm->context;
+	int idx;
+
+retry:
+	spin_lock(&mm_ctx->bd_emupage_lock);
+
+	/* Ensure we have an allocation bitmap */
+	if (!mm_ctx->bd_emupage_allocmap) {
+		mm_ctx->bd_emupage_allocmap = bitmap_zalloc(emupage_frame_count,
+							    GFP_ATOMIC);
+		if (!mm_ctx->bd_emupage_allocmap) {
+			idx = BD_EMUFRAME_NONE;
+			goto out_unlock;
+		}
+	}
+
+	/* Attempt to allocate a single bit/frame */
+	idx = bitmap_find_free_region(mm_ctx->bd_emupage_allocmap,
+				      emupage_frame_count, 0);
+	if (idx < 0) {
+		/*
+		 * Failed to allocate a frame. We'll wait until one becomes
+		 * available. We unlock the page so that other threads actually
+		 * get the opportunity to free their frames, which means
+		 * technically the result of bitmap_full may be incorrect.
+		 * However the worst case is that we repeat all this and end up
+		 * back here again.
+		 */
+		spin_unlock(&mm_ctx->bd_emupage_lock);
+		if (!wait_event_killable(mm_ctx->bd_emupage_queue,
+			!bitmap_full(mm_ctx->bd_emupage_allocmap,
+				     emupage_frame_count)))
+			goto retry;
+
+		/* Received a fatal signal - just give in */
+		return BD_EMUFRAME_NONE;
+	}
+
+	/* Success! */
+	pr_debug("allocate emuframe %d to %d\n", idx, current->pid);
+out_unlock:
+	spin_unlock(&mm_ctx->bd_emupage_lock);
+	return idx;
+}
+
+static void free_emuframe(int idx, struct mm_struct *mm)
+{
+	mm_context_t *mm_ctx = &mm->context;
+
+	spin_lock(&mm_ctx->bd_emupage_lock);
+
+	pr_debug("free emuframe %d from %d\n", idx, current->pid);
+	bitmap_clear(mm_ctx->bd_emupage_allocmap, idx, 1);
+
+	/* If some thread is waiting for a frame, now's its chance */
+	wake_up(&mm_ctx->bd_emupage_queue);
+
+	spin_unlock(&mm_ctx->bd_emupage_lock);
+}
+
+static bool within_emuframe(struct pt_regs *regs)
+{
+	unsigned long base = (unsigned long)dsemul_page();
+
+	if (regs->cp0_epc < base)
+		return false;
+	if (regs->cp0_epc >= (base + PAGE_SIZE))
+		return false;
+
+	return true;
+}
+
+bool dsemul_thread_cleanup(struct task_struct *tsk)
+{
+	int fr_idx;
+
+	/* Clear any allocated frame, retrieving its index */
+	fr_idx = atomic_xchg(&tsk->thread.bd_emu_frame, BD_EMUFRAME_NONE);
+
+	/* If no frame was allocated, we're done */
+	if (fr_idx == BD_EMUFRAME_NONE)
+		return false;
+
+	task_lock(tsk);
+
+	/* Free the frame that this thread had allocated */
+	if (tsk->mm)
+		free_emuframe(fr_idx, tsk->mm);
+
+	task_unlock(tsk);
+	return true;
+}
+
+bool dsemul_thread_rollback(struct pt_regs *regs)
+{
+	struct emuframe __user *fr;
+	int fr_idx;
+
+	/* Do nothing if we're not executing from a frame */
+	if (!within_emuframe(regs))
+		return false;
+
+	/* Find the frame being executed */
+	fr_idx = atomic_read(&current->thread.bd_emu_frame);
+	if (fr_idx == BD_EMUFRAME_NONE)
+		return false;
+	fr = &dsemul_page()[fr_idx];
+
+	/*
+	 * If the PC is at the emul instruction, roll back to the branch. If
+	 * PC is at the badinst (break) instruction, we've already emulated the
+	 * instruction so progress to the continue PC. If it's anything else
+	 * then something is amiss & the user has branched into some other area
+	 * of the emupage - we'll free the allocated frame anyway.
+	 */
+	if (msk_isa16_mode(regs->cp0_epc) == (unsigned long)&fr->emul)
+		regs->cp0_epc = current->thread.bd_emu_branch_pc;
+	else if (msk_isa16_mode(regs->cp0_epc) == (unsigned long)&fr->badinst)
+		regs->cp0_epc = current->thread.bd_emu_cont_pc;
+
+	atomic_set(&current->thread.bd_emu_frame, BD_EMUFRAME_NONE);
+	free_emuframe(fr_idx, current->mm);
+	return true;
+}
+
+void dsemul_mm_cleanup(struct mm_struct *mm)
+{
+	mm_context_t *mm_ctx = &mm->context;
+
+	bitmap_free(mm_ctx->bd_emupage_allocmap);
+}
+
+int mips_dsemul(struct pt_regs *regs, mips_instruction ir,
+		unsigned long branch_pc, unsigned long cont_pc)
+{
+	int isa16 = get_isa16_mode(regs->cp0_epc);
+	mips_instruction break_math;
+	unsigned long fr_uaddr;
+	struct emuframe fr;
+	int fr_idx, ret;
+
+	/* NOP is easy */
+	if (ir == 0)
+		return -1;
+
+	/* microMIPS instructions */
+	if (isa16) {
+		union mips_instruction insn = { .word = ir };
+
+		/* NOP16 aka MOVE16 $0, $0 */
+		if ((ir >> 16) == MM_NOP16)
+			return -1;
+
+		/* ADDIUPC */
+		if (insn.mm_a_format.opcode == mm_addiupc_op) {
+			unsigned int rs;
+			s32 v;
+
+			rs = (((insn.mm_a_format.rs + 0xe) & 0xf) + 2);
+			v = regs->cp0_epc & ~3;
+			v += insn.mm_a_format.simmediate << 2;
+			regs->regs[rs] = (long)v;
+			return -1;
+		}
+	}
+
+	pr_debug("dsemul 0x%08lx cont at 0x%08lx\n", regs->cp0_epc, cont_pc);
+
+	/* Allocate a frame if we don't already have one */
+	fr_idx = atomic_read(&current->thread.bd_emu_frame);
+	if (fr_idx == BD_EMUFRAME_NONE)
+		fr_idx = alloc_emuframe();
+	if (fr_idx == BD_EMUFRAME_NONE)
+		return SIGBUS;
+
+	/* Retrieve the appropriately encoded break instruction */
+	break_math = BREAK_MATH(isa16);
+
+	/* Write the instructions to the frame */
+	if (isa16) {
+		union mips_instruction _emul = {
+			.halfword = { ir >> 16, ir }
+		};
+		union mips_instruction _badinst = {
+			.halfword = { break_math >> 16, break_math }
+		};
+
+		fr.emul = _emul.word;
+		fr.badinst = _badinst.word;
+	} else {
+		fr.emul = ir;
+		fr.badinst = break_math;
+	}
+
+	/* Write the frame to user memory */
+	fr_uaddr = (unsigned long)&dsemul_page()[fr_idx];
+	ret = access_process_vm(current, fr_uaddr, &fr, sizeof(fr),
+				FOLL_FORCE | FOLL_WRITE);
+	if (unlikely(ret != sizeof(fr))) {
+		MIPS_FPU_EMU_INC_STATS(errors);
+		free_emuframe(fr_idx, current->mm);
+		return SIGBUS;
+	}
+
+	/* Record the PC of the branch, PC to continue from & frame index */
+	current->thread.bd_emu_branch_pc = branch_pc;
+	current->thread.bd_emu_cont_pc = cont_pc;
+	atomic_set(&current->thread.bd_emu_frame, fr_idx);
+
+	/* Change user register context to execute the frame */
+	regs->cp0_epc = fr_uaddr | isa16;
+
+	return 0;
+}
+
+bool do_dsemulret(struct pt_regs *xcp)
+{
+	/* Cleanup the allocated frame, returning if there wasn't one */
+	if (!dsemul_thread_cleanup(current)) {
+		MIPS_FPU_EMU_INC_STATS(errors);
+		return false;
+	}
+
+	/* Set EPC to return to post-branch instruction */
+	xcp->cp0_epc = current->thread.bd_emu_cont_pc;
+	pr_debug("dsemulret to 0x%08lx\n", xcp->cp0_epc);
+	MIPS_FPU_EMU_INC_STATS(ds_emul);
+	return true;
+}