Merge tag 'powerpc-5.2-6' of git://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux
Pull powerpc fixes from Michael Ellerman:
"One fix for a bug in our context id handling on 64-bit hash CPUs,
which can lead to unrelated processes being able to read/write to each
other's virtual memory. See the commit for full details.
That is the fix for CVE-2019-12817.
This also adds a kernel selftest for the bug"
* tag 'powerpc-5.2-6' of git://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux:
selftests/powerpc: Add test of fork with mapping above 512TB
powerpc/mm/64s/hash: Reallocate context ids on fork
diff --git a/arch/powerpc/mm/book3s64/mmu_context.c b/arch/powerpc/mm/book3s64/mmu_context.c
index bb70391..794404d 100644
--- a/arch/powerpc/mm/book3s64/mmu_context.c
+++ b/arch/powerpc/mm/book3s64/mmu_context.c
@@ -50,20 +50,52 @@
void slb_setup_new_exec(void);
+static int realloc_context_ids(mm_context_t *ctx)
+{
+ int i, id;
+
+ /*
+ * id 0 (aka. ctx->id) is special, we always allocate a new one, even if
+ * there wasn't one allocated previously (which happens in the exec
+ * case where ctx is newly allocated).
+ *
+ * We have to be a bit careful here. We must keep the existing ids in
+ * the array, so that we can test if they're non-zero to decide if we
+ * need to allocate a new one. However in case of error we must free the
+ * ids we've allocated but *not* any of the existing ones (or risk a
+ * UAF). That's why we decrement i at the start of the error handling
+ * loop, to skip the id that we just tested but couldn't reallocate.
+ */
+ for (i = 0; i < ARRAY_SIZE(ctx->extended_id); i++) {
+ if (i == 0 || ctx->extended_id[i]) {
+ id = hash__alloc_context_id();
+ if (id < 0)
+ goto error;
+
+ ctx->extended_id[i] = id;
+ }
+ }
+
+ /* The caller expects us to return id */
+ return ctx->id;
+
+error:
+ for (i--; i >= 0; i--) {
+ if (ctx->extended_id[i])
+ ida_free(&mmu_context_ida, ctx->extended_id[i]);
+ }
+
+ return id;
+}
+
static int hash__init_new_context(struct mm_struct *mm)
{
int index;
- index = hash__alloc_context_id();
- if (index < 0)
- return index;
-
mm->context.hash_context = kmalloc(sizeof(struct hash_mm_context),
GFP_KERNEL);
- if (!mm->context.hash_context) {
- ida_free(&mmu_context_ida, index);
+ if (!mm->context.hash_context)
return -ENOMEM;
- }
/*
* The old code would re-promote on fork, we don't do that when using
@@ -91,13 +123,20 @@
mm->context.hash_context->spt = kmalloc(sizeof(struct subpage_prot_table),
GFP_KERNEL);
if (!mm->context.hash_context->spt) {
- ida_free(&mmu_context_ida, index);
kfree(mm->context.hash_context);
return -ENOMEM;
}
}
#endif
+ }
+ index = realloc_context_ids(&mm->context);
+ if (index < 0) {
+#ifdef CONFIG_PPC_SUBPAGE_PROT
+ kfree(mm->context.hash_context->spt);
+#endif
+ kfree(mm->context.hash_context);
+ return index;
}
pkey_mm_init(mm);
diff --git a/tools/testing/selftests/powerpc/mm/.gitignore b/tools/testing/selftests/powerpc/mm/.gitignore
index ba91930..d503b87 100644
--- a/tools/testing/selftests/powerpc/mm/.gitignore
+++ b/tools/testing/selftests/powerpc/mm/.gitignore
@@ -3,4 +3,5 @@
tempfile
prot_sao
segv_errors
-wild_bctr
\ No newline at end of file
+wild_bctr
+large_vm_fork_separation
\ No newline at end of file
diff --git a/tools/testing/selftests/powerpc/mm/Makefile b/tools/testing/selftests/powerpc/mm/Makefile
index 43d6842..f1fbc15 100644
--- a/tools/testing/selftests/powerpc/mm/Makefile
+++ b/tools/testing/selftests/powerpc/mm/Makefile
@@ -2,7 +2,8 @@
noarg:
$(MAKE) -C ../
-TEST_GEN_PROGS := hugetlb_vs_thp_test subpage_prot prot_sao segv_errors wild_bctr
+TEST_GEN_PROGS := hugetlb_vs_thp_test subpage_prot prot_sao segv_errors wild_bctr \
+ large_vm_fork_separation
TEST_GEN_FILES := tempfile
top_srcdir = ../../../../..
@@ -13,6 +14,7 @@
$(OUTPUT)/prot_sao: ../utils.c
$(OUTPUT)/wild_bctr: CFLAGS += -m64
+$(OUTPUT)/large_vm_fork_separation: CFLAGS += -m64
$(OUTPUT)/tempfile:
dd if=/dev/zero of=$@ bs=64k count=1
diff --git a/tools/testing/selftests/powerpc/mm/large_vm_fork_separation.c b/tools/testing/selftests/powerpc/mm/large_vm_fork_separation.c
new file mode 100644
index 0000000..2363a7f
--- /dev/null
+++ b/tools/testing/selftests/powerpc/mm/large_vm_fork_separation.c
@@ -0,0 +1,87 @@
+// SPDX-License-Identifier: GPL-2.0+
+//
+// Copyright 2019, Michael Ellerman, IBM Corp.
+//
+// Test that allocating memory beyond the memory limit and then forking is
+// handled correctly, ie. the child is able to access the mappings beyond the
+// memory limit and the child's writes are not visible to the parent.
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/mman.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+#include "utils.h"
+
+
+#ifndef MAP_FIXED_NOREPLACE
+#define MAP_FIXED_NOREPLACE MAP_FIXED // "Should be safe" above 512TB
+#endif
+
+
+static int test(void)
+{
+ int p2c[2], c2p[2], rc, status, c, *p;
+ unsigned long page_size;
+ pid_t pid;
+
+ page_size = sysconf(_SC_PAGESIZE);
+ SKIP_IF(page_size != 65536);
+
+ // Create a mapping at 512TB to allocate an extended_id
+ p = mmap((void *)(512ul << 40), page_size, PROT_READ | PROT_WRITE,
+ MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED_NOREPLACE, -1, 0);
+ if (p == MAP_FAILED) {
+ perror("mmap");
+ printf("Error: couldn't mmap(), confirm kernel has 4TB support?\n");
+ return 1;
+ }
+
+ printf("parent writing %p = 1\n", p);
+ *p = 1;
+
+ FAIL_IF(pipe(p2c) == -1 || pipe(c2p) == -1);
+
+ pid = fork();
+ if (pid == 0) {
+ FAIL_IF(read(p2c[0], &c, 1) != 1);
+
+ pid = getpid();
+ printf("child writing %p = %d\n", p, pid);
+ *p = pid;
+
+ FAIL_IF(write(c2p[1], &c, 1) != 1);
+ FAIL_IF(read(p2c[0], &c, 1) != 1);
+ exit(0);
+ }
+
+ c = 0;
+ FAIL_IF(write(p2c[1], &c, 1) != 1);
+ FAIL_IF(read(c2p[0], &c, 1) != 1);
+
+ // Prevent compiler optimisation
+ barrier();
+
+ rc = 0;
+ printf("parent reading %p = %d\n", p, *p);
+ if (*p != 1) {
+ printf("Error: BUG! parent saw child's write! *p = %d\n", *p);
+ rc = 1;
+ }
+
+ FAIL_IF(write(p2c[1], &c, 1) != 1);
+ FAIL_IF(waitpid(pid, &status, 0) == -1);
+ FAIL_IF(!WIFEXITED(status) || WEXITSTATUS(status));
+
+ if (rc == 0)
+ printf("success: test completed OK\n");
+
+ return rc;
+}
+
+int main(void)
+{
+ return test_harness(test, "large_vm_fork_separation");
+}
