4.9-stable review patch. If anyone has any objections, please let me know.
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From: Will Deacon will.deacon@arm.com
commit 6bd288569b50bc89fa5513031086746968f585cb upstream.
Debug exception handlers may be called for exceptions generated both by user and kernel code. In many cases, this is checked explicitly, but in other cases things either happen to work by happy accident or they go slightly wrong. For example, executing 'brk #4' from userspace will enter the kprobes code and be ignored, but the instruction will be retried forever in userspace instead of delivering a SIGTRAP.
Fix this issue in the most stable-friendly fashion by simply adding explicit checks of the triggering exception level to all of our debug exception handlers.
Cc: stable@vger.kernel.org Reviewed-by: Mark Rutland mark.rutland@arm.com Signed-off-by: Will Deacon will.deacon@arm.com Signed-off-by: Catalin Marinas catalin.marinas@arm.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/arm64/kernel/kgdb.c | 15 ++++++++++++--- arch/arm64/kernel/probes/kprobes.c | 6 ++++++ 2 files changed, 18 insertions(+), 3 deletions(-)
--- a/arch/arm64/kernel/kgdb.c +++ b/arch/arm64/kernel/kgdb.c @@ -231,24 +231,33 @@ int kgdb_arch_handle_exception(int excep
static int kgdb_brk_fn(struct pt_regs *regs, unsigned int esr) { + if (user_mode(regs)) + return DBG_HOOK_ERROR; + kgdb_handle_exception(1, SIGTRAP, 0, regs); - return 0; + return DBG_HOOK_HANDLED; } NOKPROBE_SYMBOL(kgdb_brk_fn)
static int kgdb_compiled_brk_fn(struct pt_regs *regs, unsigned int esr) { + if (user_mode(regs)) + return DBG_HOOK_ERROR; + compiled_break = 1; kgdb_handle_exception(1, SIGTRAP, 0, regs);
- return 0; + return DBG_HOOK_HANDLED; } NOKPROBE_SYMBOL(kgdb_compiled_brk_fn);
static int kgdb_step_brk_fn(struct pt_regs *regs, unsigned int esr) { + if (user_mode(regs)) + return DBG_HOOK_ERROR; + kgdb_handle_exception(1, SIGTRAP, 0, regs); - return 0; + return DBG_HOOK_HANDLED; } NOKPROBE_SYMBOL(kgdb_step_brk_fn);
--- a/arch/arm64/kernel/probes/kprobes.c +++ b/arch/arm64/kernel/probes/kprobes.c @@ -450,6 +450,9 @@ kprobe_single_step_handler(struct pt_reg struct kprobe_ctlblk *kcb = get_kprobe_ctlblk(); int retval;
+ if (user_mode(regs)) + return DBG_HOOK_ERROR; + /* return error if this is not our step */ retval = kprobe_ss_hit(kcb, instruction_pointer(regs));
@@ -466,6 +469,9 @@ kprobe_single_step_handler(struct pt_reg int __kprobes kprobe_breakpoint_handler(struct pt_regs *regs, unsigned int esr) { + if (user_mode(regs)) + return DBG_HOOK_ERROR; + kprobe_handler(regs); return DBG_HOOK_HANDLED; }