linux-kernel - [PATCH] KVM: arm64: vgic-its: Remove VLA usage

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Date:   Fri, 29 Jun 2018 11:46:18 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Christoffer Dall <christoffer.dall@....com>
Cc:     Marc Zyngier <marc.zyngier@....com>,
        Eric Auger <eric.auger@...hat.com>,
        Andre Przywara <andre.przywara@....com>,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-kernel@...r.kernel.org
Subject: [PATCH] KVM: arm64: vgic-its: Remove VLA usage

In the quest to remove all stack VLA usage from the kernel[1], this
switches to using a maximum size and adds sanity checks. Additionally
cleans up some of the int-vs-u32 usage and adds additional bounds checking.
As it currently stands, this will always be 8 bytes until the ABI changes.

[1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com

Cc: Christoffer Dall <christoffer.dall@....com>
Cc: Marc Zyngier <marc.zyngier@....com>
Cc: Eric Auger <eric.auger@...hat.com>
Cc: Andre Przywara <andre.przywara@....com>
Cc: linux-arm-kernel@...ts.infradead.org
Cc: kvmarm@...ts.cs.columbia.edu
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 virt/kvm/arm/vgic/vgic-its.c | 19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/virt/kvm/arm/vgic/vgic-its.c b/virt/kvm/arm/vgic/vgic-its.c
index 4ed79c939fb4..3143fc047fcf 100644
--- a/virt/kvm/arm/vgic/vgic-its.c
+++ b/virt/kvm/arm/vgic/vgic-its.c
@@ -168,8 +168,14 @@ struct vgic_its_abi {
 	int (*commit)(struct vgic_its *its);
 };
 
+#define ABI_0_ESZ	8
+#define ESZ_MAX		ABI_0_ESZ
+
 static const struct vgic_its_abi its_table_abi_versions[] = {
-	[0] = {.cte_esz = 8, .dte_esz = 8, .ite_esz = 8,
+	[0] = {
+	 .cte_esz = ABI_0_ESZ,
+	 .dte_esz = ABI_0_ESZ,
+	 .ite_esz = ABI_0_ESZ,
 	 .save_tables = vgic_its_save_tables_v0,
 	 .restore_tables = vgic_its_restore_tables_v0,
 	 .commit = vgic_its_commit_v0,
@@ -180,10 +186,12 @@ static const struct vgic_its_abi its_table_abi_versions[] = {
 
 inline const struct vgic_its_abi *vgic_its_get_abi(struct vgic_its *its)
 {
+	if (WARN_ON(its->abi_rev >= NR_ITS_ABIS))
+		return NULL;
 	return &its_table_abi_versions[its->abi_rev];
 }
 
-int vgic_its_set_abi(struct vgic_its *its, int rev)
+static int vgic_its_set_abi(struct vgic_its *its, u32 rev)
 {
 	const struct vgic_its_abi *abi;
 
@@ -1881,16 +1889,19 @@ typedef int (*entry_fn_t)(struct vgic_its *its, u32 id, void *entry,
  * Return: < 0 on error, 0 if last element was identified, 1 otherwise
  * (the last element may not be found on second level tables)
  */
-static int scan_its_table(struct vgic_its *its, gpa_t base, int size, int esz,
+static int scan_its_table(struct vgic_its *its, gpa_t base, int size, u32 esz,
 			  int start_id, entry_fn_t fn, void *opaque)
 {
 	struct kvm *kvm = its->dev->kvm;
 	unsigned long len = size;
 	int id = start_id;
 	gpa_t gpa = base;
-	char entry[esz];
+	char entry[ESZ_MAX];
 	int ret;
 
+	if (WARN_ON(esz > ESZ_MAX))
+		return -EINVAL;
+
 	memset(entry, 0, esz);
 
 	while (len > 0) {
-- 
2.17.1


-- 
Kees Cook
Pixel Security