linux-kernel - [PATCH 09/33] x86/fpu: Change 'size_total' parameter to unsigned and standardize the size checks in copy_xstate_to

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Date:   Sat, 23 Sep 2017 14:59:52 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     linux-kernel@...r.kernel.org
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Eric Biggers <ebiggers3@...il.com>,
        Andy Lutomirski <luto@...capital.net>,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        "H . Peter Anvin" <hpa@...or.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Oleg Nesterov <oleg@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Rik van Riel <riel@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Yu-cheng Yu <yu-cheng.yu@...el.com>
Subject: [PATCH 09/33] x86/fpu: Change 'size_total' parameter to unsigned and standardize the size checks in copy_xstate_to_*()

'size_total' is derived from an unsigned input parameter - and then converted
to 'int' and checked for negative ranges:

	if (size_total < 0 || offset < size_total) {

This conversion and the checks are unnecessary obfuscation, reject overly
large requested copy sizes outright and simplify the underlying code.

Reported-by: Rik van Riel <riel@...hat.com>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Fenghua Yu <fenghua.yu@...el.com>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Oleg Nesterov <oleg@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Yu-cheng Yu <yu-cheng.yu@...el.com>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/kernel/fpu/xstate.c | 32 +++++++++++++++-----------------
 1 file changed, 15 insertions(+), 17 deletions(-)

diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index c13083579655..b18c5457065a 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -925,15 +925,11 @@ int arch_set_user_pkey_access(struct task_struct *tsk, int pkey,
  * the source data pointer or increment pos, count, kbuf, and ubuf.
  */
 static inline int
-__copy_xstate_to_kernel(void *kbuf,
-			const void *data,
-			unsigned int offset, unsigned int size, int size_total)
+__copy_xstate_to_kernel(void *kbuf, const void *data,
+			unsigned int offset, unsigned int size, unsigned int size_total)
 {
-	if (!size)
-		return 0;
-
-	if (size_total < 0 || offset < size_total) {
-		unsigned int copy = size_total < 0 ? size : min(size, size_total - offset);
+	if (offset < size_total) {
+		unsigned int copy = min(size, size_total - offset);
 
 		memcpy(kbuf + offset, data, copy);
 	}
@@ -986,12 +982,13 @@ int copy_xstate_to_kernel(void *kbuf, struct xregs_state *xsave, unsigned int of
 			offset = xstate_offsets[i];
 			size = xstate_sizes[i];
 
+			/* The next component has to fit fully into the output buffer: */
+			if (offset + size > size_total)
+				break;
+
 			ret = __copy_xstate_to_kernel(kbuf, src, offset, size, size_total);
 			if (ret)
 				return ret;
-
-			if (offset + size >= size_total)
-				break;
 		}
 
 	}
@@ -1010,13 +1007,13 @@ int copy_xstate_to_kernel(void *kbuf, struct xregs_state *xsave, unsigned int of
 }
 
 static inline int
-__copy_xstate_to_user(void __user *ubuf, const void *data, unsigned int offset, unsigned int size, int size_total)
+__copy_xstate_to_user(void __user *ubuf, const void *data, unsigned int offset, unsigned int size, unsigned int size_total)
 {
 	if (!size)
 		return 0;
 
-	if (size_total < 0 || offset < size_total) {
-		unsigned int copy = size_total < 0 ? size : min(size, size_total - offset);
+	if (offset < size_total) {
+		unsigned int copy = min(size, size_total - offset);
 
 		if (__copy_to_user(ubuf + offset, data, copy))
 			return -EFAULT;
@@ -1069,12 +1066,13 @@ int copy_xstate_to_user(void __user *ubuf, struct xregs_state *xsave, unsigned i
 			offset = xstate_offsets[i];
 			size = xstate_sizes[i];
 
+			/* The next component has to fit fully into the output buffer: */
+			if (offset + size > size_total)
+				break;
+
 			ret = __copy_xstate_to_user(ubuf, src, offset, size, size_total);
 			if (ret)
 				return ret;
-
-			if (offset + size >= size_total)
-				break;
 		}
 
 	}
-- 
2.11.0