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arm64: debug: Ensure debug handlers check triggering exception level

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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>
This commit is contained in:
Will Deacon 2019-03-01 13:28:01 +00:00 committed by Catalin Marinas
parent b9a4b9d084
commit 6bd288569b
2 changed files with 16 additions and 4 deletions
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14
arch/arm64/kernel/kgdb.c
View File

@ -244,27 +244,33 @@ int kgdb_arch_handle_exception(int exception_vector, int signo,
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 (!kgdb_single_step)
if (user_mode(regs) || !kgdb_single_step)
return DBG_HOOK_ERROR;
kgdb_handle_exception(1, SIGTRAP, 0, regs);
return 0;
return DBG_HOOK_HANDLED;
}
NOKPROBE_SYMBOL(kgdb_step_brk_fn);

6
arch/arm64/kernel/probes/kprobes.c
View File

@ -450,6 +450,9 @@ kprobe_single_step_handler(struct pt_regs *regs, unsigned int esr)
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_regs *regs, unsigned int esr)
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;
}