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From: nadav.amit@gmail.com
To: Peter Zijlstra <peterz@infradead.org>,
	Borislav Petkov <bp@alien8.de>, Andy Lutomirski <luto@kernel.org>,
	Ingo Molnar <mingo@redhat.com>
Cc: linux-kernel@vger.kernel.org, x86@kernel.org, hpa@zytor.com,
	Thomas Gleixner <tglx@linutronix.de>,
	Nadav Amit <nadav.amit@gmail.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	linux_dti@icloud.com, linux-integrity@vger.kernel.org,
	linux-security-module@vger.kernel.org, akpm@linux-foundation.org,
	kernel-hardening@lists.openwall.com, linux-mm@kvack.org,
	will.deacon@arm.com, ard.biesheuvel@linaro.org,
	kristen@linux.intel.com, deneen.t.dock@intel.com,
	Rick Edgecombe <rick.p.edgecombe@intel.com>,
	Nadav Amit <namit@vmware.com>
Subject: [PATCH v6 09/24] x86/kgdb: Avoid redundant comparison of patched code
Date: Fri, 26 Apr 2019 16:22:48 -0700	[thread overview]
Message-ID: <20190426232303.28381-10-nadav.amit@gmail.com> (raw)
In-Reply-To: <20190426232303.28381-1-nadav.amit@gmail.com>

From: Nadav Amit <namit@vmware.com>

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.

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Nadav Amit <namit@vmware.com>
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
---
 arch/x86/kernel/kgdb.c | 14 +-------------
 1 file changed, 1 insertion(+), 13 deletions(-)

diff --git a/arch/x86/kernel/kgdb.c b/arch/x86/kernel/kgdb.c
index 2b203ee5b879..13b13311b792 100644
--- 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,
-- 
2.17.1

  parent reply	other threads:[~2019-04-26 23:22 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-04-26 23:22 [PATCH v6 00/24] x86: text_poke() fixes and executable lockdowns nadav.amit
2019-04-26 23:22 ` [PATCH v6 01/24] Fix "x86/alternatives: Lockdep-enforce text_mutex in text_poke*()" nadav.amit
2019-04-26 23:22 ` [PATCH v6 02/24] x86/jump_label: Use text_poke_early() during early init nadav.amit
2019-04-26 23:22 ` [PATCH v6 03/24] x86/mm: Introduce temporary mm structs nadav.amit
2019-04-26 23:22 ` [PATCH v6 04/24] x86/mm: Save debug registers when loading a temporary mm nadav.amit
2019-04-26 23:22 ` [PATCH v6 05/24] uprobes: Initialize uprobes earlier nadav.amit
2019-04-26 23:22 ` [PATCH v6 06/24] fork: Provide a function for copying init_mm nadav.amit
2019-04-26 23:22 ` [PATCH v6 07/24] x86/alternative: Initialize temporary mm for patching nadav.amit
2019-04-26 23:22 ` [PATCH v6 08/24] x86/alternative: Use temporary mm for text poking nadav.amit
2019-04-26 23:22 ` nadav.amit [this message]
2019-04-26 23:22 ` [PATCH v6 10/24] x86/ftrace: Set trampoline pages as executable nadav.amit
2019-04-26 23:22 ` [PATCH v6 11/24] x86/kprobes: Set instruction page " nadav.amit
2019-04-26 23:22 ` [PATCH v6 12/24] x86/module: Avoid breaking W^X while loading modules nadav.amit
2019-04-26 23:22 ` [PATCH v6 13/24] x86/jump-label: Remove support for custom poker nadav.amit
2019-04-26 23:22 ` [PATCH v6 14/24] x86/alternative: Remove the return value of text_poke_*() nadav.amit
2019-04-26 23:22 ` [PATCH v6 15/24] x86/mm/cpa: Add set_direct_map_ functions nadav.amit
2019-04-26 23:22 ` [PATCH v6 16/24] mm: Make hibernate handle unmapped pages nadav.amit
2019-04-26 23:22 ` [PATCH v6 17/24] vmalloc: Add flag for free of special permsissions nadav.amit
2019-04-26 23:22 ` [PATCH v6 18/24] modules: Use vmalloc special flag nadav.amit
2019-04-26 23:22 ` [PATCH v6 19/24] bpf: " nadav.amit
2019-04-26 23:22 ` [PATCH v6 20/24] x86/ftrace: " nadav.amit
2019-04-26 23:23 ` [PATCH v6 21/24] x86/kprobes: " nadav.amit
2019-04-26 23:23 ` [PATCH v6 22/24] x86/alternative: Comment about module removal races nadav.amit
2019-04-26 23:23 ` [PATCH v6 23/24] mm/tlb: Provide default nmi_uaccess_okay() nadav.amit
2019-04-26 23:23 ` [PATCH v6 24/24] bpf: Fail bpf_probe_write_user() while mm is switched nadav.amit
2019-04-27 10:22 ` [PATCH v6 00/24] x86: text_poke() fixes and executable lockdowns Ingo Molnar
2019-04-27 10:32 ` Peter Zijlstra

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