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powerpc/watchpoint: Disable watchpoint hit by larx/stcx instructions

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If watchpoint exception is generated by larx/stcx instructions, the
reservation created by larx gets lost while handling exception, and
thus stcx instruction always fails. Generally these instructions are
used in a while(1) loop, for example spinlocks. And because stcx
never succeeds, it loops forever and ultimately hangs the system.

Note that ptrace anyway works in one-shot mode and thus for ptrace
we don't change the behaviour. It's up to ptrace user to take care
of this.

Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.ibm.com>
Acked-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20190910131513.30499-1-ravi.bangoria@linux.ibm.com
This commit is contained in:
Ravi Bangoria 2019-09-10 18:45:13 +05:30 committed by Michael Ellerman
parent 587164cd59
commit bc01bdf6c5
1 changed files with 34 additions and 17 deletions
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51
arch/powerpc/kernel/hw_breakpoint.c
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@ -195,14 +195,32 @@ void thread_change_pc(struct task_struct *tsk, struct pt_regs *regs)
tsk->thread.last_hit_ubp = NULL;
}
static bool is_larx_stcx_instr(struct pt_regs *regs, unsigned int instr)
{
int ret, type;
struct instruction_op op;
ret = analyse_instr(&op, regs, instr);
type = GETTYPE(op.type);
return (!ret && (type == LARX || type == STCX));
}
/*
* Handle debug exception notifications.
*/
static bool stepping_handler(struct pt_regs *regs, struct perf_event *bp,
unsigned long addr)
{
int stepped;
unsigned int instr;
unsigned int instr = 0;
if (__get_user_inatomic(instr, (unsigned int *)regs->nip))
goto fail;
if (is_larx_stcx_instr(regs, instr)) {
printk_ratelimited("Breakpoint hit on instruction that can't be emulated."
" Breakpoint at 0x%lx will be disabled.\n", addr);
goto disable;
}
/* Do not emulate user-space instructions, instead single-step them */
if (user_mode(regs)) {
@ -211,23 +229,22 @@ static bool stepping_handler(struct pt_regs *regs, struct perf_event *bp,
return false;
}
stepped = 0;
instr = 0;
if (!__get_user_inatomic(instr, (unsigned int *)regs->nip))
stepped = emulate_step(regs, instr);
if (!emulate_step(regs, instr))
goto fail;
/*
* emulate_step() could not execute it. We've failed in reliably
* handling the hw-breakpoint. Unregister it and throw a warning
* message to let the user know about it.
*/
if (!stepped) {
WARN(1, "Unable to handle hardware breakpoint. Breakpoint at "
"0x%lx will be disabled.", addr);
perf_event_disable_inatomic(bp);
return false;
}
return true;
fail:
/*
* We've failed in reliably handling the hw-breakpoint. Unregister
* it and throw a warning message to let the user know about it.
*/
WARN(1, "Unable to handle hardware breakpoint. Breakpoint at "
"0x%lx will be disabled.", addr);
disable:
perf_event_disable_inatomic(bp);
return false;
}
int hw_breakpoint_handler(struct die_args *args)