riscv: Only consider swbp/ss handlers for correct privileged mode

RISC-V software breakpoint trap handlers are used for {k,u}probes.

When trapping from kernelmode, only the kernelmode handlers should be
considered. Vice versa, only usermode handlers for usermode
traps. This is not the case on RISC-V, which can trigger a bug if a
userspace process uses uprobes, and a WARN() is triggered from
kernelmode (which is implemented via {c.,}ebreak).

The kernel will trap on the kernelmode {c.,}ebreak, look for uprobes
handlers, realize incorrectly that uprobes need to be handled, and
exit the trap handler early. The trap returns to re-executing the
{c.,}ebreak, and enter an infinite trap-loop.

The issue was found running the BPF selftest [1].

Fix this issue by only considering the swbp/ss handlers for
kernel/usermode respectively. Also, move CONFIG ifdeffery from traps.c
to the asm/{k,u}probes.h headers.

Note that linux/uprobes.h only include asm/uprobes.h if CONFIG_UPROBES
is defined, which is why asm/uprobes.h needs to be unconditionally
included in traps.c

Link: https://lore.kernel.org/linux-riscv/87v8d19aun.fsf@all.your.base.are.belong.to.us/
Fixes: 74784081aac8 ("riscv: Add uprobes supported")
Reviewed-by: Guo Ren <guoren@kernel.org>
Reviewed-by: Nam Cao <namcaov@gmail.com>
Tested-by: Puranjay Mohan <puranjay12@gmail.com>
Signed-off-by: Björn Töpel <bjorn@rivosinc.com>
Link: https://lore.kernel.org/r/20230912065619.62020-1-bjorn@kernel.org
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

diff --git a/arch/riscv/include/asm/kprobes.h b/arch/riscv/include/asm/kprobes.h
index e7882ccb0fd46a67da4e9e1d287066b121c5f188..78ea44f767189214c9c3263c93e10c4c1db91bb8 100644 (file)
--- a/arch/riscv/include/asm/kprobes.h
+++ b/arch/riscv/include/asm/kprobes.h
@@ -40,6 +40,15 @@ void arch_remove_kprobe(struct kprobe *p);
 int kprobe_fault_handler(struct pt_regs *regs, unsigned int trapnr);
 bool kprobe_breakpoint_handler(struct pt_regs *regs);
 bool kprobe_single_step_handler(struct pt_regs *regs);
-
+#else
+static inline bool kprobe_breakpoint_handler(struct pt_regs *regs)
+{
+       return false;
+}
+
+static inline bool kprobe_single_step_handler(struct pt_regs *regs)
+{
+       return false;
+}
 #endif /* CONFIG_KPROBES */
 #endif /* _ASM_RISCV_KPROBES_H */

diff --git a/arch/riscv/include/asm/uprobes.h b/arch/riscv/include/asm/uprobes.h
index f2183e00fdd20946052009f05d857e99191bcb40..3fc7deda9190251510f96d952c5276a900912676 100644 (file)
--- a/arch/riscv/include/asm/uprobes.h
+++ b/arch/riscv/include/asm/uprobes.h
@@ -34,7 +34,18 @@ struct arch_uprobe {
        bool simulate;
 };
 
+#ifdef CONFIG_UPROBES
 bool uprobe_breakpoint_handler(struct pt_regs *regs);
 bool uprobe_single_step_handler(struct pt_regs *regs);
-
+#else
+static inline bool uprobe_breakpoint_handler(struct pt_regs *regs)
+{
+       return false;
+}
+
+static inline bool uprobe_single_step_handler(struct pt_regs *regs)
+{
+       return false;
+}
+#endif /* CONFIG_UPROBES */
 #endif /* _ASM_RISCV_UPROBES_H */

diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c
index 19807c4d3805d4d6b308b5a74cada73a5ef0dbf3..fae8f610d867fd7f34ec19ed24e7cb3da06b968e 100644 (file)
--- a/arch/riscv/kernel/traps.c
+++ b/arch/riscv/kernel/traps.c
@@ -13,6 +13,8 @@
 #include <linux/kdebug.h>
 #include <linux/uaccess.h>
 #include <linux/kprobes.h>
+#include <linux/uprobes.h>
+#include <asm/uprobes.h>
 #include <linux/mm.h>
 #include <linux/module.h>
 #include <linux/irq.h>
@@ -247,22 +249,28 @@ static inline unsigned long get_break_insn_length(unsigned long pc)
        return GET_INSN_LENGTH(insn);
 }
 
+static bool probe_single_step_handler(struct pt_regs *regs)
+{
+       bool user = user_mode(regs);
+
+       return user ? uprobe_single_step_handler(regs) : kprobe_single_step_handler(regs);
+}
+
+static bool probe_breakpoint_handler(struct pt_regs *regs)
+{
+       bool user = user_mode(regs);
+
+       return user ? uprobe_breakpoint_handler(regs) : kprobe_breakpoint_handler(regs);
+}
+
 void handle_break(struct pt_regs *regs)
 {
-#ifdef CONFIG_KPROBES
-       if (kprobe_single_step_handler(regs))
+       if (probe_single_step_handler(regs))
                return;
 
-       if (kprobe_breakpoint_handler(regs))
-               return;
-#endif
-#ifdef CONFIG_UPROBES
-       if (uprobe_single_step_handler(regs))
+       if (probe_breakpoint_handler(regs))
                return;
 
-       if (uprobe_breakpoint_handler(regs))
-               return;
-#endif
        current->thread.bad_cause = regs->cause;
 
        if (user_mode(regs))