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powerpc/watchpoint: Fix exception handling for CONFIG_HAVE_HW_BREAKPOINT=N

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On powerpc, ptrace watchpoint works in one-shot mode. i.e. kernel
disables event every time it fires and user has to re-enable it.
Also, in case of ptrace watchpoint, kernel notifies ptrace user
before executing instruction.

With CONFIG_HAVE_HW_BREAKPOINT=N, kernel is missing to disable
ptrace event and thus it's causing infinite loop of exceptions.
This is especially harmful when user watches on a data which is
also read/written by kernel, eg syscall parameters. In such case,
infinite exceptions happens in kernel mode which causes soft-lockup.

Fixes: 9422de3e95 ("powerpc: Hardware breakpoints rewrite to handle non DABR breakpoint registers")
Reported-by: Pedro Miraglia Franco de Carvalho <pedromfc@linux.ibm.com>
Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200902042945.129369-6-ravi.bangoria@linux.ibm.com
This commit is contained in:
Ravi Bangoria
2020-09-02 09:59:42 +05:30
committed by Michael Ellerman
parent edc8dd99b2
commit 5b905d7798
3 changed files with 54 additions and 1 deletions
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3
arch/powerpc/include/asm/hw_breakpoint.h
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@ -18,6 +18,7 @@ struct arch_hw_breakpoint {
u16 type;
u16 len; /* length of the target data symbol */
u16 hw_len; /* length programmed in hw */
u8 flags;
};
/* Note: Don't change the first 6 bits below as they are in the same order
@ -37,6 +38,8 @@ struct arch_hw_breakpoint {
#define HW_BRK_TYPE_PRIV_ALL (HW_BRK_TYPE_USER | HW_BRK_TYPE_KERNEL | \
HW_BRK_TYPE_HYP)
#define HW_BRK_FLAG_DISABLED 0x1
/* Minimum granularity */
#ifdef CONFIG_PPC_8xx
#define HW_BREAKPOINT_SIZE 0x4