[PATCH v2 1/2] powerpc/hugetlb: Handle mmap_min_addr correctly in get_unmapped_area callback

After we ALIGN up the address we need to make sure we didn't overflow
and resulted in zero address. In that case, we need to make sure that
the returned address is greater than mmap_min_addr.

This fixes selftest va_128TBswitch --run-hugetlb reporting failures when
run as non root user for

mmap(-1, MAP_HUGETLB)

The bug is that a non-root user requesting address -1 will be given address 0
which will then fail, whereas they should have been given something else that
would have succeeded.

We also avoid the first mmap(-1, MAP_HUGETLB) returning NULL address as mmap address
with this change. So we think this is not a security issue, because it only affects
whether we choose an address below mmap_min_addr, not whether we
actually allow that address to be mapped. ie. there are existing capability
checks to prevent a user mapping below mmap_min_addr and those will still be
honoured even without this fix.

Fixes: 484837601d4d ("powerpc/mm: Add radix support for hugetlb")
Reviewed-by: Laurent Dufour <redacted>
Signed-off-by: Aneesh Kumar K.V <redacted>
---
 arch/powerpc/mm/hugetlbpage-radix.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/mm/hugetlbpage-radix.c b/arch/powerpc/mm/hugetlbpage-radix.c
index 2486bee0f93e..97c7a39ebc00 100644
--- a/arch/powerpc/mm/hugetlbpage-radix.c
+++ b/arch/powerpc/mm/hugetlbpage-radix.c

@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0
 #include <linux/mm.h>
 #include <linux/hugetlb.h>
+#include <linux/security.h>
 #include <asm/pgtable.h>
 #include <asm/pgalloc.h>
 #include <asm/cacheflush.h>

@@ -73,7 +74,7 @@ radix__hugetlb_get_unmapped_area(struct file *file, unsigned long addr,
 	if (addr) {
 		addr = ALIGN(addr, huge_page_size(h));
 		vma = find_vma(mm, addr);
-		if (high_limit - len >= addr &&
+		if (high_limit - len >= addr && addr >= mmap_min_addr &&
 		    (!vma || addr + len <= vm_start_gap(vma)))
 			return addr;
 	}

@@ -83,7 +84,7 @@ radix__hugetlb_get_unmapped_area(struct file *file, unsigned long addr,
 	 */
 	info.flags = VM_UNMAPPED_AREA_TOPDOWN;
 	info.length = len;
-	info.low_limit = PAGE_SIZE;
+	info.low_limit = max(PAGE_SIZE, mmap_min_addr);
 	info.high_limit = mm->mmap_base + (high_limit - DEFAULT_MAP_WINDOW);
 	info.align_mask = PAGE_MASK & ~huge_page_mask(h);
 	info.align_offset = 0;

-- 
2.20.1

When doing top-down search the low_limit is not PAGE_SIZE but rather
max(PAGE_SIZE, mmap_min_addr). This handle cases in which mmap_min_addr >
PAGE_SIZE.

Fixes: fba2369e6ceb ("mm: use vm_unmapped_area() on powerpc architecture")
Reviewed-by: Laurent Dufour <redacted>
Signed-off-by: Aneesh Kumar K.V <redacted>
---
 arch/powerpc/mm/slice.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/arch/powerpc/mm/slice.c b/arch/powerpc/mm/slice.c
index 06898c13901d..aec91dbcdc0b 100644
--- a/arch/powerpc/mm/slice.c
+++ b/arch/powerpc/mm/slice.c

@@ -32,6 +32,7 @@
 #include <linux/export.h>
 #include <linux/hugetlb.h>
 #include <linux/sched/mm.h>
+#include <linux/security.h>
 #include <asm/mman.h>
 #include <asm/mmu.h>
 #include <asm/copro.h>

@@ -377,6 +378,7 @@ static unsigned long slice_find_area_topdown(struct mm_struct *mm,
 	int pshift = max_t(int, mmu_psize_defs[psize].shift, PAGE_SHIFT);
 	unsigned long addr, found, prev;
 	struct vm_unmapped_area_info info;
+	unsigned long min_addr = max(PAGE_SIZE, mmap_min_addr);
 
 	info.flags = VM_UNMAPPED_AREA_TOPDOWN;
 	info.length = len;

@@ -393,7 +395,7 @@ static unsigned long slice_find_area_topdown(struct mm_struct *mm,
 	if (high_limit > DEFAULT_MAP_WINDOW)
 		addr += mm->context.slb_addr_limit - DEFAULT_MAP_WINDOW;
 
-	while (addr > PAGE_SIZE) {
+	while (addr > min_addr) {
 		info.high_limit = addr;
 		if (!slice_scan_available(addr - 1, available, 0, &addr))
 			continue;

@@ -405,8 +407,8 @@ static unsigned long slice_find_area_topdown(struct mm_struct *mm,
 		 * Check if we need to reduce the range, or if we can
 		 * extend it to cover the previous available slice.
 		 */
-		if (addr < PAGE_SIZE)
-			addr = PAGE_SIZE;
+		if (addr < min_addr)
+			addr = min_addr;
 		else if (slice_scan_available(addr - 1, available, 0, &prev)) {
 			addr = prev;
 			goto prev_slice;

@@ -528,7 +530,7 @@ unsigned long slice_get_unmapped_area(unsigned long addr, unsigned long len,
 		addr = _ALIGN_UP(addr, page_size);
 		slice_dbg(" aligned addr=%lx\n", addr);
 		/* Ignore hint if it's too large or overlaps a VMA */
-		if (addr > high_limit - len ||
+		if (addr > high_limit - len || addr < mmap_min_addr ||
 		    !slice_area_is_free(mm, addr, len))
 			addr = 0;
 	}

-- 
2.20.1

On Tue, 2019-02-26 at 04:39:34 UTC, "Aneesh Kumar K.V" wrote:

After we ALIGN up the address we need to make sure we didn't overflow
and resulted in zero address. In that case, we need to make sure that
the returned address is greater than mmap_min_addr.

This fixes selftest va_128TBswitch --run-hugetlb reporting failures when
run as non root user for

mmap(-1, MAP_HUGETLB)

The bug is that a non-root user requesting address -1 will be given address 0
which will then fail, whereas they should have been given something else that
would have succeeded.

We also avoid the first mmap(-1, MAP_HUGETLB) returning NULL address as mmap address
with this change. So we think this is not a security issue, because it only affects
whether we choose an address below mmap_min_addr, not whether we
actually allow that address to be mapped. ie. there are existing capability
checks to prevent a user mapping below mmap_min_addr and those will still be
honoured even without this fix.

Fixes: 484837601d4d ("powerpc/mm: Add radix support for hugetlb")
Reviewed-by: Laurent Dufour <redacted>
Signed-off-by: Aneesh Kumar K.V <redacted>

Series applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/5330367fa300742a97e20e953b1f77f4

cheers