powerpc/kuap: Fix set direction in allow/prevent_user_access()

__builtin_constant_p() always return 0 for pointers, so on RADIX we always end up opening both direction (by writing 0 in SPR29): 0000000000000170 <._copy_to_user>: ... 1b0: 4c 00 01 2c isync 1b4: 39 20 00 00 li r9,0 1b8: 7d 3d 03 a6 mtspr 29,r9 1bc: 4c 00 01 2c isync 1c0: 48 00 00 01 bl 1c0 <._copy_to_user+0x50> 1c0: R_PPC64_REL24 .__copy_tofrom_user ... 0000000000000220 <._copy_from_user>: ... 2ac: 4c 00 01 2c isync 2b0: 39 20 00 00 li r9,0 2b4: 7d 3d 03 a6 mtspr 29,r9 2b8: 4c 00 01 2c isync 2bc: 7f c5 f3 78 mr r5,r30 2c0: 7f 83 e3 78 mr r3,r28 2c4: 48 00 00 01 bl 2c4 <._copy_from_user+0xa4> 2c4: R_PPC64_REL24 .__copy_tofrom_user ... Use an explicit parameter for direction selection, so that GCC is able to see it is a constant: 00000000000001b0 <._copy_to_user>: ... 1f0: 4c 00 01 2c isync 1f4: 3d 20 40 00 lis r9,16384 1f8: 79 29 07 c6 rldicr r9,r9,32,31 1fc: 7d 3d 03 a6 mtspr 29,r9 200: 4c 00 01 2c isync 204: 48 00 00 01 bl 204 <._copy_to_user+0x54> 204: R_PPC64_REL24 .__copy_tofrom_user ... 0000000000000260 <._copy_from_user>: ... 2ec: 4c 00 01 2c isync 2f0: 39 20 ff ff li r9,-1 2f4: 79 29 00 04 rldicr r9,r9,0,0 2f8: 7d 3d 03 a6 mtspr 29,r9 2fc: 4c 00 01 2c isync 300: 7f c5 f3 78 mr r5,r30 304: 7f 83 e3 78 mr r3,r28 308: 48 00 00 01 bl 308 <._copy_from_user+0xa8> 308: R_PPC64_REL24 .__copy_tofrom_user ... Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr> [mpe: Spell out the directions, s/KUAP_R/KUAP_READ/ etc.] Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/f4e88ec4941d5facb35ce75026b0112f980086c3.1579866752.git.christophe.leroy@c-s.fr
mariux64 · Jan 28, 2020 · 1d8f739 · 1d8f739
1 parent 6ec20aa
commit 1d8f739
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Showing 5 changed files with 43 additions and 19 deletions.
diff --git a/arch/powerpc/include/asm/book3s/32/kup.h b/arch/powerpc/include/asm/book3s/32/kup.h
@@ -102,11 +102,13 @@ static inline void kuap_update_sr(u32 sr, u32 addr, u32 end)
 	isync();	/* Context sync required after mtsrin() */
 }
 
-static inline void allow_user_access(void __user *to, const void __user *from, u32 size)
+static __always_inline void allow_user_access(void __user *to, const void __user *from,
+					      u32 size, unsigned long dir)
 {
 	u32 addr, end;
 
-	if (__builtin_constant_p(to) && to == NULL)
+	BUILD_BUG_ON(!__builtin_constant_p(dir));
+	if (!(dir & KUAP_WRITE))
 		return;
 
 	addr = (__force u32)to;
@@ -119,11 +121,16 @@ static inline void allow_user_access(void __user *to, const void __user *from, u
 	kuap_update_sr(mfsrin(addr) & ~SR_KS, addr, end);	/* Clear Ks */
 }
 
-static inline void prevent_user_access(void __user *to, const void __user *from, u32 size)
+static __always_inline void prevent_user_access(void __user *to, const void __user *from,
+						u32 size, unsigned long dir)
 {
 	u32 addr = (__force u32)to;
 	u32 end = min(addr + size, TASK_SIZE);
 
+	BUILD_BUG_ON(!__builtin_constant_p(dir));
+	if (!(dir & KUAP_WRITE))
+		return;
+
 	if (!addr || addr >= TASK_SIZE || !size)
 		return;
 

diff --git a/arch/powerpc/include/asm/book3s/64/kup-radix.h b/arch/powerpc/include/asm/book3s/64/kup-radix.h
@@ -77,20 +77,21 @@ static inline void set_kuap(unsigned long value)
 	isync();
 }
 
-static inline void allow_user_access(void __user *to, const void __user *from,
-				     unsigned long size)
+static __always_inline void allow_user_access(void __user *to, const void __user *from,
+					      unsigned long size, unsigned long dir)
 {
 	// This is written so we can resolve to a single case at build time
-	if (__builtin_constant_p(to) && to == NULL)
+	BUILD_BUG_ON(!__builtin_constant_p(dir));
+	if (dir == KUAP_READ)
 		set_kuap(AMR_KUAP_BLOCK_WRITE);
-	else if (__builtin_constant_p(from) && from == NULL)
+	else if (dir == KUAP_WRITE)
 		set_kuap(AMR_KUAP_BLOCK_READ);
 	else
 		set_kuap(0);
 }
 
 static inline void prevent_user_access(void __user *to, const void __user *from,
-				       unsigned long size)
+				       unsigned long size, unsigned long dir)
 {
 	set_kuap(AMR_KUAP_BLOCKED);
 }

diff --git a/arch/powerpc/include/asm/kup.h b/arch/powerpc/include/asm/kup.h
@@ -2,6 +2,10 @@
 #ifndef _ASM_POWERPC_KUP_H_
 #define _ASM_POWERPC_KUP_H_
 
+#define KUAP_READ	1
+#define KUAP_WRITE	2
+#define KUAP_READ_WRITE	(KUAP_READ | KUAP_WRITE)
+
 #ifdef CONFIG_PPC64
 #include <asm/book3s/64/kup-radix.h>
 #endif
@@ -42,9 +46,9 @@ void setup_kuap(bool disabled);
 #else
 static inline void setup_kuap(bool disabled) { }
 static inline void allow_user_access(void __user *to, const void __user *from,
-				     unsigned long size) { }
+				     unsigned long size, unsigned long dir) { }
 static inline void prevent_user_access(void __user *to, const void __user *from,
-				       unsigned long size) { }
+				       unsigned long size, unsigned long dir) { }
 static inline bool
 bad_kuap_fault(struct pt_regs *regs, unsigned long address, bool is_write)
 {
@@ -54,24 +58,36 @@ bad_kuap_fault(struct pt_regs *regs, unsigned long address, bool is_write)
 
 static inline void allow_read_from_user(const void __user *from, unsigned long size)
 {
-	allow_user_access(NULL, from, size);
+	allow_user_access(NULL, from, size, KUAP_READ);
 }
 
 static inline void allow_write_to_user(void __user *to, unsigned long size)
 {
-	allow_user_access(to, NULL, size);
+	allow_user_access(to, NULL, size, KUAP_WRITE);
+}
+
+static inline void allow_read_write_user(void __user *to, const void __user *from,
+					 unsigned long size)
+{
+	allow_user_access(to, from, size, KUAP_READ_WRITE);
 }
 
 static inline void prevent_read_from_user(const void __user *from, unsigned long size)
 {
-	prevent_user_access(NULL, from, size);
+	prevent_user_access(NULL, from, size, KUAP_READ);
 }
 
 static inline void prevent_write_to_user(void __user *to, unsigned long size)
 {
-	prevent_user_access(to, NULL, size);
+	prevent_user_access(to, NULL, size, KUAP_WRITE);
+}
+
+static inline void prevent_read_write_user(void __user *to, const void __user *from,
+					   unsigned long size)
+{
+	prevent_user_access(to, from, size, KUAP_READ_WRITE);
 }
 
 #endif /* !__ASSEMBLY__ */
 
-#endif /* _ASM_POWERPC_KUP_H_ */
+#endif /* _ASM_POWERPC_KUAP_H_ */
diff --git a/arch/powerpc/include/asm/nohash/32/kup-8xx.h b/arch/powerpc/include/asm/nohash/32/kup-8xx.h
@@ -35,13 +35,13 @@
 #include <asm/reg.h>
 
 static inline void allow_user_access(void __user *to, const void __user *from,
-				     unsigned long size)
+				     unsigned long size, unsigned long dir)
 {
 	mtspr(SPRN_MD_AP, MD_APG_INIT);
 }
 
 static inline void prevent_user_access(void __user *to, const void __user *from,
-				       unsigned long size)
+				       unsigned long size, unsigned long dir)
 {
 	mtspr(SPRN_MD_AP, MD_APG_KUAP);
 }

diff --git a/arch/powerpc/include/asm/uaccess.h b/arch/powerpc/include/asm/uaccess.h
@@ -313,9 +313,9 @@ raw_copy_in_user(void __user *to, const void __user *from, unsigned long n)
 	unsigned long ret;
 
 	barrier_nospec();
-	allow_user_access(to, from, n);
+	allow_read_write_user(to, from, n);
 	ret = __copy_tofrom_user(to, from, n);
-	prevent_user_access(to, from, n);
+	prevent_read_write_user(to, from, n);
 	return ret;
 }
 #endif /* __powerpc64__ */