[PATCH v2 10/10] arm64: vdso: Map the vDSO text with guarded pages when built for BTI

Mark Brown
2020-04-29T21:23:31Z

The kernel is responsible for mapping the vDSO into userspace processes,
including mapping the text section as executable. Handle the mapping of
the vDSO for BTI similarly, mapping the text section as guarded pages so
the BTI annotations in the vDSO become effective when they are present.

This will mean that we can have BTI active for the vDSO in processes that
do not otherwise support BTI. This should not be an issue for any expected
use of the vDSO.

Signed-off-by: Mark Brown <broonie@kernel.org>
---
arch/arm64/kernel/vdso.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kernel/vdso.c b/arch/arm64/kernel/vdso.c
index 354b11e27c07..9271b7774df0 100644
--- a/arch/arm64/kernel/vdso.c
+++ b/arch/arm64/kernel/vdso.c
@@ -142,6 +142,7 @@ static int __setup_additional_pages(enum arch_vdso_type arch_index,
int uses_interp)
{
unsigned long vdso_base, vdso_text_len, vdso_mapping_len;
+ unsigned long gp_flags = 0;
void *ret;

vdso_text_len = vdso_lookup[arch_index].vdso_pages << PAGE_SHIFT;
@@ -160,10 +161,13 @@ static int __setup_additional_pages(enum arch_vdso_type arch_index,
if (IS_ERR(ret))
goto up_fail;

+ if (IS_ENABLED(CONFIG_ARM64_BTI_KERNEL) && system_supports_bti())
+ gp_flags = VM_ARM64_BTI;
+
vdso_base += PAGE_SIZE;
mm->context.vdso = (void *)vdso_base;
ret = _install_special_mapping(mm, vdso_base, vdso_text_len,
- VM_READ|VM_EXEC|
+ VM_READ|VM_EXEC|gp_flags|
VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC,
vdso_lookup[arch_index].cm);
if (IS_ERR(ret))
--
2.20.1