Re: [PATCH v6 3/8] powerpc/watchpoint/ptrace: Fix SETHWDEBUG when CONFIG_HAVE_HW_BREAKPOINT=N

From: Rogerio Alves
Date: Thu Sep 17 2020 - 11:03:27 EST

On 9/2/20 1:29 AM, Ravi Bangoria wrote:
When kernel is compiled with CONFIG_HAVE_HW_BREAKPOINT=N, user can
still create watchpoint using PPC_PTRACE_SETHWDEBUG, with limited
functionalities. But, such watchpoints are never firing because of
the missing privilege settings. Fix that.

It's safe to set HW_BRK_TYPE_PRIV_ALL because we don't really leak
any kernel address in signal info. Setting HW_BRK_TYPE_PRIV_ALL will
also help to find scenarios when kernel accesses user memory.

Reported-by: Pedro Miraglia Franco de Carvalho <pedromfc@xxxxxxxxxxxxx>
Suggested-by: Pedro Miraglia Franco de Carvalho <pedromfc@xxxxxxxxxxxxx>
Signed-off-by: Ravi Bangoria <ravi.bangoria@xxxxxxxxxxxxx>
Tested-by: Rogerio Alves <rcardoso@xxxxxxxxxxxxx>
arch/powerpc/kernel/ptrace/ptrace-noadv.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/kernel/ptrace/ptrace-noadv.c b/arch/powerpc/kernel/ptrace/ptrace-noadv.c
index 697c7e4b5877..57a0ab822334 100644
--- a/arch/powerpc/kernel/ptrace/ptrace-noadv.c
+++ b/arch/powerpc/kernel/ptrace/ptrace-noadv.c
@@ -217,7 +217,7 @@ long ppc_set_hwdebug(struct task_struct *child, struct ppc_hw_breakpoint *bp_inf
return -EIO;
brk.address = ALIGN_DOWN(bp_info->addr, HW_BREAKPOINT_SIZE);
brk.len = DABR_MAX_LEN;
if (bp_info->trigger_type & PPC_BREAKPOINT_TRIGGER_READ)
brk.type |= HW_BRK_TYPE_READ;