On 7/19/2021 11:21 AM, Edgecombe, Rick P wrote:
On Fri, 2021-05-21 at 15:15 -0700, Yu-cheng Yu wrote:
From: "H.J. Lu" <hjl.tools@xxxxxxxxx>
Update ARCH_X86_CET_STATUS and ARCH_X86_CET_DISABLE for Indirect
Branch
Tracking.
Signed-off-by: H.J. Lu <hjl.tools@xxxxxxxxx>
Signed-off-by: Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx>
Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
arch/x86/kernel/cet_prctl.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/arch/x86/kernel/cet_prctl.c
b/arch/x86/kernel/cet_prctl.c
index b426d200e070..bd3c80d402e7 100644
--- a/arch/x86/kernel/cet_prctl.c
+++ b/arch/x86/kernel/cet_prctl.c
@@ -22,6 +22,9 @@ static int cet_copy_status_to_user(struct
thread_shstk *shstk, u64 __user *ubuf)
buf[2] = shstk->size;
}
+ if (shstk->ibt)
+ buf[0] |= GNU_PROPERTY_X86_FEATURE_1_IBT;
+
Can you have IBT enabled but not shadow stack via kernel parameters?
Outside this diff it has:
if (!cpu_feature_enabled(X86_FEATURE_SHSTK))
return -ENOTSUPP;
If shadow stack is disabled by the kernel parameter, IBT is also disabled.
So if "no_user_shstk" is set, this can't be used for IBT. But the
kernel would attempt to enable IBT.
It will not.
Also if so, the CR4 bit enabling logic needs adjusting in this IBT
series. If not, we should probably mention this in the docs and enforce
it. It would then follow the logic in Kconfig, so maybe the simplest.
Like maybe instead of no_user_shstk, just no_user_cet?
If shadow stack is disabled (from either Kconfig or kernel
command-line), then IBT is also disabled. However, we still need two
kernel parameters because no_user_ibt can be useful sometimes. I will
add a sentence in the document to indicate that IBT depends on shadow
stack.
Thanks,
Yu-cheng
