powerpc fixes for 5.2 #6

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.
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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
This commit is contained in:
Linus Torvalds 2019-06-24 21:20:39 +08:00
commit 26df62aaae
4 changed files with 139 additions and 10 deletions

View File

@ -50,20 +50,52 @@ EXPORT_SYMBOL_GPL(hash__alloc_context_id);
void slb_setup_new_exec(void); 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) static int hash__init_new_context(struct mm_struct *mm)
{ {
int index; int index;
index = hash__alloc_context_id();
if (index < 0)
return index;
mm->context.hash_context = kmalloc(sizeof(struct hash_mm_context), mm->context.hash_context = kmalloc(sizeof(struct hash_mm_context),
GFP_KERNEL); GFP_KERNEL);
if (!mm->context.hash_context) { if (!mm->context.hash_context)
ida_free(&mmu_context_ida, index);
return -ENOMEM; return -ENOMEM;
}
/* /*
* The old code would re-promote on fork, we don't do that when using * The old code would re-promote on fork, we don't do that when using
@ -91,13 +123,20 @@ static int hash__init_new_context(struct mm_struct *mm)
mm->context.hash_context->spt = kmalloc(sizeof(struct subpage_prot_table), mm->context.hash_context->spt = kmalloc(sizeof(struct subpage_prot_table),
GFP_KERNEL); GFP_KERNEL);
if (!mm->context.hash_context->spt) { if (!mm->context.hash_context->spt) {
ida_free(&mmu_context_ida, index);
kfree(mm->context.hash_context); kfree(mm->context.hash_context);
return -ENOMEM; return -ENOMEM;
} }
} }
#endif #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); pkey_mm_init(mm);

View File

@ -3,4 +3,5 @@ subpage_prot
tempfile tempfile
prot_sao prot_sao
segv_errors segv_errors
wild_bctr wild_bctr
large_vm_fork_separation

View File

@ -2,7 +2,8 @@
noarg: noarg:
$(MAKE) -C ../ $(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 TEST_GEN_FILES := tempfile
top_srcdir = ../../../../.. top_srcdir = ../../../../..
@ -13,6 +14,7 @@ $(TEST_GEN_PROGS): ../harness.c
$(OUTPUT)/prot_sao: ../utils.c $(OUTPUT)/prot_sao: ../utils.c
$(OUTPUT)/wild_bctr: CFLAGS += -m64 $(OUTPUT)/wild_bctr: CFLAGS += -m64
$(OUTPUT)/large_vm_fork_separation: CFLAGS += -m64
$(OUTPUT)/tempfile: $(OUTPUT)/tempfile:
dd if=/dev/zero of=$@ bs=64k count=1 dd if=/dev/zero of=$@ bs=64k count=1

View File

@ -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");
}