[PATCH] x86/fsgsbase/64: Use TASK_SIZE_MAX for FSBASE/GSBASE upper limits

[Andy Lutomirski]

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@xxxxxxxxxx>
---
 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