[PATCH 5/6] arm64/vdso: Restrict splitting VVAR VMA

From: Andrei Vagin
Date: Wed Jun 24 2020 - 04:33:37 EST


Forbid splitting VVAR VMA resulting in a stricter ABI and reducing the
amount of corner-cases to consider while working further on VDSO time
namespace support.

As the offset from timens to VVAR page is computed compile-time, the pages
in VVAR should stay together and not being partically mremap()'ed.

Reviewed-by: Vincenzo Frascino <vincenzo.frascino@xxxxxxx>
Reviewed-by: Dmitry Safonov <dima@xxxxxxxxxx>
Signed-off-by: Andrei Vagin <avagin@xxxxxxxxx>
---
arch/arm64/kernel/vdso.c | 13 +++++++++++++
1 file changed, 13 insertions(+)

diff --git a/arch/arm64/kernel/vdso.c b/arch/arm64/kernel/vdso.c
index be9ca8c46cff..8be6bd6625db 100644
--- a/arch/arm64/kernel/vdso.c
+++ b/arch/arm64/kernel/vdso.c
@@ -224,6 +224,17 @@ static vm_fault_t vvar_fault(const struct vm_special_mapping *sm,
return vmf_insert_pfn(vma, vmf->address, pfn);
}

+static int vvar_mremap(const struct vm_special_mapping *sm,
+ struct vm_area_struct *new_vma)
+{
+ unsigned long new_size = new_vma->vm_end - new_vma->vm_start;
+
+ if (new_size != VVAR_NR_PAGES * PAGE_SIZE)
+ return -EINVAL;
+
+ return 0;
+}
+
static int __setup_additional_pages(enum vdso_abi abi,
struct mm_struct *mm,
struct linux_binprm *bprm,
@@ -306,6 +317,7 @@ static struct vm_special_mapping aarch32_vdso_maps[] = {
[AA32_MAP_VVAR] = {
.name = "[vvar]",
.fault = vvar_fault,
+ .mremap = vvar_mremap,
},
[AA32_MAP_VDSO] = {
.name = "[vdso]",
@@ -474,6 +486,7 @@ static struct vm_special_mapping aarch64_vdso_maps[] __ro_after_init = {
[AA64_MAP_VVAR] = {
.name = "[vvar]",
.fault = vvar_fault,
+ .mremap = vvar_mremap,
},
[AA64_MAP_VDSO] = {
.name = "[vdso]",
--
2.24.1