linux-kernel - [PATCH v3 03/15] powerpc/align: Convert emulate_spe() to user_access

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Message-Id: <c95a648fdf75992c9d88f3c73cc23e7537fcf2ad.1615555354.git.christophe.leroy@csgroup.eu>
Date:   Fri, 12 Mar 2021 13:25:11 +0000 (UTC)
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Daniel Axtens <dja@...ens.net>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH v3 03/15] powerpc/align: Convert emulate_spe() to user_access_begin

This patch converts emulate_spe() to using user_access_begin
logic.

Since commit 662bbcb2747c ("mm, sched: Allow uaccess in atomic with
pagefault_disable()"), might_fault() doesn't fire when called from
sections where pagefaults are disabled, which must be the case
when using _inatomic variants of __get_user and __put_user. So
the might_fault() in user_access_begin() is not a problem.

There was a verification of user_mode() together with the access_ok(),
but there is a second verification of user_mode() just after, that
leads to immediate return. The access_ok() is now part of the
user_access_begin which is called after that other user_mode()
verification, so no need to check user_mode() again.

Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
Reviewed-by: Daniel Axtens <dja@...ens.net>
---
v3:
- Changed the second user_read_access_begin() to user_write_access_begin()
- Reworded explaination about the user_mode() with access_ok() in the commit message
---
 arch/powerpc/kernel/align.c | 61 ++++++++++++++++++++-----------------
 1 file changed, 33 insertions(+), 28 deletions(-)

diff --git a/arch/powerpc/kernel/align.c b/arch/powerpc/kernel/align.c
index c7797eb958c7..f362c99213be 100644
--- a/arch/powerpc/kernel/align.c
+++ b/arch/powerpc/kernel/align.c
@@ -107,7 +107,6 @@ static struct aligninfo spe_aligninfo[32] = {
 static int emulate_spe(struct pt_regs *regs, unsigned int reg,
 		       struct ppc_inst ppc_instr)
 {
-	int ret;
 	union {
 		u64 ll;
 		u32 w[2];
@@ -127,11 +126,6 @@ static int emulate_spe(struct pt_regs *regs, unsigned int reg,
 	nb = spe_aligninfo[instr].len;
 	flags = spe_aligninfo[instr].flags;
 
-	/* Verify the address of the operand */
-	if (unlikely(user_mode(regs) &&
-		     !access_ok(addr, nb)))
-		return -EFAULT;
-
 	/* userland only */
 	if (unlikely(!user_mode(regs)))
 		return 0;
@@ -169,26 +163,27 @@ static int emulate_spe(struct pt_regs *regs, unsigned int reg,
 		}
 	} else {
 		temp.ll = data.ll = 0;
-		ret = 0;
 		p = addr;
 
+		if (!user_read_access_begin(addr, nb))
+			return -EFAULT;
+
 		switch (nb) {
 		case 8:
-			ret |= __get_user_inatomic(temp.v[0], p++);
-			ret |= __get_user_inatomic(temp.v[1], p++);
-			ret |= __get_user_inatomic(temp.v[2], p++);
-			ret |= __get_user_inatomic(temp.v[3], p++);
+			unsafe_get_user(temp.v[0], p++, Efault_read);
+			unsafe_get_user(temp.v[1], p++, Efault_read);
+			unsafe_get_user(temp.v[2], p++, Efault_read);
+			unsafe_get_user(temp.v[3], p++, Efault_read);
 			fallthrough;
 		case 4:
-			ret |= __get_user_inatomic(temp.v[4], p++);
-			ret |= __get_user_inatomic(temp.v[5], p++);
+			unsafe_get_user(temp.v[4], p++, Efault_read);
+			unsafe_get_user(temp.v[5], p++, Efault_read);
 			fallthrough;
 		case 2:
-			ret |= __get_user_inatomic(temp.v[6], p++);
-			ret |= __get_user_inatomic(temp.v[7], p++);
-			if (unlikely(ret))
-				return -EFAULT;
+			unsafe_get_user(temp.v[6], p++, Efault_read);
+			unsafe_get_user(temp.v[7], p++, Efault_read);
 		}
+		user_read_access_end();
 
 		switch (instr) {
 		case EVLDD:
@@ -255,31 +250,41 @@ static int emulate_spe(struct pt_regs *regs, unsigned int reg,
 
 	/* Store result to memory or update registers */
 	if (flags & ST) {
-		ret = 0;
 		p = addr;
+
+		if (!user_write_access_begin(addr, nb))
+			return -EFAULT;
+
 		switch (nb) {
 		case 8:
-			ret |= __put_user_inatomic(data.v[0], p++);
-			ret |= __put_user_inatomic(data.v[1], p++);
-			ret |= __put_user_inatomic(data.v[2], p++);
-			ret |= __put_user_inatomic(data.v[3], p++);
+			unsafe_put_user(data.v[0], p++, Efault_write);
+			unsafe_put_user(data.v[1], p++, Efault_write);
+			unsafe_put_user(data.v[2], p++, Efault_write);
+			unsafe_put_user(data.v[3], p++, Efault_write);
 			fallthrough;
 		case 4:
-			ret |= __put_user_inatomic(data.v[4], p++);
-			ret |= __put_user_inatomic(data.v[5], p++);
+			unsafe_put_user(data.v[4], p++, Efault_write);
+			unsafe_put_user(data.v[5], p++, Efault_write);
 			fallthrough;
 		case 2:
-			ret |= __put_user_inatomic(data.v[6], p++);
-			ret |= __put_user_inatomic(data.v[7], p++);
+			unsafe_put_user(data.v[6], p++, Efault_write);
+			unsafe_put_user(data.v[7], p++, Efault_write);
 		}
-		if (unlikely(ret))
-			return -EFAULT;
+		user_write_access_end();
 	} else {
 		*evr = data.w[0];
 		regs->gpr[reg] = data.w[1];
 	}
 
 	return 1;
+
+Efault_read:
+	user_read_access_end();
+	return -EFAULT;
+
+Efault_write:
+	user_write_access_end();
+	return -EFAULT;
 }
 #endif /* CONFIG_SPE */
 
-- 
2.25.0