x86/kgdb: Avoid redundant comparison of patched code

text_poke() already ensures that the written value is the correct one
and fails if that is not the case. There is no need for an additional
comparison. Remove it.

Signed-off-by: Nadav Amit <namit@vmware.com>
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: <akpm@linux-foundation.org>
Cc: <ard.biesheuvel@linaro.org>
Cc: <deneen.t.dock@intel.com>
Cc: <kernel-hardening@lists.openwall.com>
Cc: <kristen@linux.intel.com>
Cc: <linux_dti@icloud.com>
Cc: <will.deacon@arm.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Rik van Riel <riel@surriel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20190426001143.4983-9-namit@vmware.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/kernel/kgdb.c b/arch/x86/kernel/kgdb.c
index 2b203ee5b8796224ab6700a11bbc1a6457c92b2f..13b13311b792564f12d0adf78d64fd770be6d16c 100644 (file)
--- a/arch/x86/kernel/kgdb.c
+++ b/arch/x86/kernel/kgdb.c
@@ -747,7 +747,6 @@ void kgdb_arch_set_pc(struct pt_regs *regs, unsigned long ip)
 int kgdb_arch_set_breakpoint(struct kgdb_bkpt *bpt)
 {
        int err;
-       char opc[BREAK_INSTR_SIZE];
 
        bpt->type = BP_BREAKPOINT;
        err = probe_kernel_read(bpt->saved_instr, (char *)bpt->bpt_addr,
@@ -766,11 +765,6 @@ int kgdb_arch_set_breakpoint(struct kgdb_bkpt *bpt)
                return -EBUSY;
        text_poke_kgdb((void *)bpt->bpt_addr, arch_kgdb_ops.gdb_bpt_instr,
                       BREAK_INSTR_SIZE);
-       err = probe_kernel_read(opc, (char *)bpt->bpt_addr, BREAK_INSTR_SIZE);
-       if (err)
-               return err;
-       if (memcmp(opc, arch_kgdb_ops.gdb_bpt_instr, BREAK_INSTR_SIZE))
-               return -EINVAL;
        bpt->type = BP_POKE_BREAKPOINT;
 
        return err;
@@ -778,9 +772,6 @@ int kgdb_arch_set_breakpoint(struct kgdb_bkpt *bpt)
 
 int kgdb_arch_remove_breakpoint(struct kgdb_bkpt *bpt)
 {
-       int err;
-       char opc[BREAK_INSTR_SIZE];
-
        if (bpt->type != BP_POKE_BREAKPOINT)
                goto knl_write;
        /*
@@ -791,10 +782,7 @@ int kgdb_arch_remove_breakpoint(struct kgdb_bkpt *bpt)
                goto knl_write;
        text_poke_kgdb((void *)bpt->bpt_addr, bpt->saved_instr,
                       BREAK_INSTR_SIZE);
-       err = probe_kernel_read(opc, (char *)bpt->bpt_addr, BREAK_INSTR_SIZE);
-       if (err || memcmp(opc, bpt->saved_instr, BREAK_INSTR_SIZE))
-               goto knl_write;
-       return err;
+       return 0;
 
 knl_write:
        return probe_kernel_write((char *)bpt->bpt_addr,