linux-kernel - [PATCH] x86/fsgsbase/64: Use TASK_SIZE

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Date:	Tue, 10 May 2016 09:18:46 -0700
From:	Andy Lutomirski <luto@...nel.org>
To:	x86@...nel.org
Cc:	linux-kernel@...r.kernel.org, Borislav Petkov <bp@...en8.de>,
	Andy Lutomirski <luto@...nel.org>
Subject: [PATCH] x86/fsgsbase/64: Use TASK_SIZE_MAX for FSBASE/GSBASE upper limits

The GSBASE upper limit exists to prevent user code from confusing
the paranoid idtentry path.  The FSBASE upper limit is just for
consistency.  There's no need to enforce a smaller limit for 32-bit
tasks.

Just use TASK_SIZE_MAX.  This simplifies the logic and will save a
few bytes of code.

Signed-off-by: Andy Lutomirski <luto@...nel.org>
---
 arch/x86/kernel/process_64.c | 4 ++--
 arch/x86/kernel/ptrace.c     | 4 ++--
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index 4285f6adcc5e..5b027ab84b8a 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -532,7 +532,7 @@ long do_arch_prctl(struct task_struct *task, int code, unsigned long addr)
 
 	switch (code) {
 	case ARCH_SET_GS:
-		if (addr >= TASK_SIZE_OF(task))
+		if (addr >= TASK_SIZE_MAX)
 			return -EPERM;
 		cpu = get_cpu();
 		task->thread.gsindex = 0;
@@ -545,7 +545,7 @@ long do_arch_prctl(struct task_struct *task, int code, unsigned long addr)
 	case ARCH_SET_FS:
 		/* Not strictly needed for fs, but do it for symmetry
 		   with gs */
-		if (addr >= TASK_SIZE_OF(task))
+		if (addr >= TASK_SIZE_MAX)
 			return -EPERM;
 		cpu = get_cpu();
 		task->thread.fsindex = 0;
diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c
index e60ef918f53d..600edd225e81 100644
--- a/arch/x86/kernel/ptrace.c
+++ b/arch/x86/kernel/ptrace.c
@@ -392,7 +392,7 @@ static int putreg(struct task_struct *child,
 
 #ifdef CONFIG_X86_64
 	case offsetof(struct user_regs_struct,fs_base):
-		if (value >= TASK_SIZE_OF(child))
+		if (value >= TASK_SIZE_MAX)
 			return -EIO;
 		/*
 		 * When changing the segment base, use do_arch_prctl
@@ -406,7 +406,7 @@ static int putreg(struct task_struct *child,
 		/*
 		 * Exactly the same here as the %fs handling above.
 		 */
-		if (value >= TASK_SIZE_OF(child))
+		if (value >= TASK_SIZE_MAX)
 			return -EIO;
 		if (child->thread.gsbase != value)
 			return do_arch_prctl(child, ARCH_SET_GS, value);
-- 
2.5.5