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    Subject[PATCH 4.14 020/343] powerpc/kgdb: add kgdb_arch_set/remove_breakpoint()
    Date
    From: Christophe Leroy <christophe.leroy@c-s.fr>

    [ Upstream commit fb978ca207743badfe7efd9eebe68bcbb4969f79 ]

    Generic implementation fails to remove breakpoints after init
    when CONFIG_STRICT_KERNEL_RWX is selected:

    [ 13.251285] KGDB: BP remove failed: c001c338
    [ 13.259587] kgdbts: ERROR PUT: end of test buffer on 'do_fork_test' line 8 expected OK got $E14#aa
    [ 13.268969] KGDB: re-enter exception: ALL breakpoints killed
    [ 13.275099] CPU: 0 PID: 1 Comm: init Not tainted 4.18.0-g82bbb913ffd8 #860
    [ 13.282836] Call Trace:
    [ 13.285313] [c60e1ba0] [c0080ef0] kgdb_handle_exception+0x6f4/0x720 (unreliable)
    [ 13.292618] [c60e1c30] [c000e97c] kgdb_handle_breakpoint+0x3c/0x98
    [ 13.298709] [c60e1c40] [c000af54] program_check_exception+0x104/0x700
    [ 13.305083] [c60e1c60] [c000e45c] ret_from_except_full+0x0/0x4
    [ 13.310845] [c60e1d20] [c02a22ac] run_simple_test+0x2b4/0x2d4
    [ 13.316532] [c60e1d30] [c0081698] put_packet+0xb8/0x158
    [ 13.321694] [c60e1d60] [c00820b4] gdb_serial_stub+0x230/0xc4c
    [ 13.327374] [c60e1dc0] [c0080af8] kgdb_handle_exception+0x2fc/0x720
    [ 13.333573] [c60e1e50] [c000e928] kgdb_singlestep+0xb4/0xcc
    [ 13.339068] [c60e1e70] [c000ae1c] single_step_exception+0x90/0xac
    [ 13.345100] [c60e1e80] [c000e45c] ret_from_except_full+0x0/0x4
    [ 13.350865] [c60e1f40] [c000e11c] ret_from_syscall+0x0/0x38
    [ 13.356346] Kernel panic - not syncing: Recursive entry to debugger

    This patch creates powerpc specific version of
    kgdb_arch_set_breakpoint() and kgdb_arch_remove_breakpoint()
    using patch_instruction()

    Fixes: 1e0fc9d1eb2b ("powerpc/Kconfig: Enable STRICT_KERNEL_RWX for some configs")
    Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
    Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    arch/powerpc/include/asm/kgdb.h | 5 +++-
    arch/powerpc/kernel/kgdb.c | 43 +++++++++++++++++++++++++++------
    2 files changed, 39 insertions(+), 9 deletions(-)

    diff --git a/arch/powerpc/include/asm/kgdb.h b/arch/powerpc/include/asm/kgdb.h
    index 9db24e77b9f4b..a9e098a3b881f 100644
    --- a/arch/powerpc/include/asm/kgdb.h
    +++ b/arch/powerpc/include/asm/kgdb.h
    @@ -26,9 +26,12 @@
    #define BREAK_INSTR_SIZE 4
    #define BUFMAX ((NUMREGBYTES * 2) + 512)
    #define OUTBUFMAX ((NUMREGBYTES * 2) + 512)
    +
    +#define BREAK_INSTR 0x7d821008 /* twge r2, r2 */
    +
    static inline void arch_kgdb_breakpoint(void)
    {
    - asm(".long 0x7d821008"); /* twge r2, r2 */
    + asm(stringify_in_c(.long BREAK_INSTR));
    }
    #define CACHE_FLUSH_IS_SAFE 1
    #define DBG_MAX_REG_NUM 70
    diff --git a/arch/powerpc/kernel/kgdb.c b/arch/powerpc/kernel/kgdb.c
    index 35e240a0a4087..59c578f865aa6 100644
    --- a/arch/powerpc/kernel/kgdb.c
    +++ b/arch/powerpc/kernel/kgdb.c
    @@ -24,6 +24,7 @@
    #include <asm/processor.h>
    #include <asm/machdep.h>
    #include <asm/debug.h>
    +#include <asm/code-patching.h>
    #include <linux/slab.h>

    /*
    @@ -144,7 +145,7 @@ static int kgdb_handle_breakpoint(struct pt_regs *regs)
    if (kgdb_handle_exception(1, SIGTRAP, 0, regs) != 0)
    return 0;

    - if (*(u32 *) (regs->nip) == *(u32 *) (&arch_kgdb_ops.gdb_bpt_instr))
    + if (*(u32 *)regs->nip == BREAK_INSTR)
    regs->nip += BREAK_INSTR_SIZE;

    return 1;
    @@ -441,16 +442,42 @@ int kgdb_arch_handle_exception(int vector, int signo, int err_code,
    return -1;
    }

    +int kgdb_arch_set_breakpoint(struct kgdb_bkpt *bpt)
    +{
    + int err;
    + unsigned int instr;
    + unsigned int *addr = (unsigned int *)bpt->bpt_addr;
    +
    + err = probe_kernel_address(addr, instr);
    + if (err)
    + return err;
    +
    + err = patch_instruction(addr, BREAK_INSTR);
    + if (err)
    + return -EFAULT;
    +
    + *(unsigned int *)bpt->saved_instr = instr;
    +
    + return 0;
    +}
    +
    +int kgdb_arch_remove_breakpoint(struct kgdb_bkpt *bpt)
    +{
    + int err;
    + unsigned int instr = *(unsigned int *)bpt->saved_instr;
    + unsigned int *addr = (unsigned int *)bpt->bpt_addr;
    +
    + err = patch_instruction(addr, instr);
    + if (err)
    + return -EFAULT;
    +
    + return 0;
    +}
    +
    /*
    * Global data
    */
    -struct kgdb_arch arch_kgdb_ops = {
    -#ifdef __LITTLE_ENDIAN__
    - .gdb_bpt_instr = {0x08, 0x10, 0x82, 0x7d},
    -#else
    - .gdb_bpt_instr = {0x7d, 0x82, 0x10, 0x08},
    -#endif
    -};
    +struct kgdb_arch arch_kgdb_ops;

    static int kgdb_not_implemented(struct pt_regs *regs)
    {
    --
    2.20.1


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