Unverified Commit 9f564b92 authored by Björn Töpel's avatar Björn Töpel Committed by Palmer Dabbelt
Browse files

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/

 # [1]
Fixes: 74784081 ("riscv: Add uprobes supported")
Reviewed-by: default avatarGuo Ren <guoren@kernel.org>
Reviewed-by: default avatarNam Cao <namcaov@gmail.com>
Tested-by: default avatarPuranjay Mohan <puranjay12@gmail.com>
Signed-off-by: default avatarBjörn Töpel <bjorn@rivosinc.com>
Link: https://lore.kernel.org/r/20230912065619.62020-1-bjorn@kernel.org


Signed-off-by: default avatarPalmer Dabbelt <palmer@rivosinc.com>
parent b06fab00

arch/riscv/include/asm/kprobes.h

+10 −1
Original line number Diff line number Diff line
@@ -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 */

arch/riscv/include/asm/uprobes.h

+12 −1
Original line number Diff line number Diff line
@@ -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 */

arch/riscv/kernel/traps.c

+18 −10
Original line number Diff line number Diff line
@@ -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))