On 9/2/2020 1:03 PM, Jann Horn wrote:
On Tue, Aug 25, 2020 at 2:30 AM Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx> wrote:
Add REGSET_CET64/REGSET_CET32 to get/set CET MSRs:
IA32_U_CET (user-mode CET settings) and
IA32_PL3_SSP (user-mode Shadow Stack)
[...]
diff --git a/arch/x86/kernel/fpu/regset.c b/arch/x86/kernel/fpu/regset.c
[...]
+int cetregs_get(struct task_struct *target, const struct user_regset *regset,
+ struct membuf to)
+{
+ struct fpu *fpu = &target->thread.fpu;
+ struct cet_user_state *cetregs;
+
+ if (!boot_cpu_has(X86_FEATURE_SHSTK))
+ return -ENODEV;
+
+ fpu__prepare_read(fpu);
+ cetregs = get_xsave_addr(&fpu->state.xsave, XFEATURE_CET_USER);
+ if (!cetregs)
+ return -EFAULT;
Can this branch ever be hit without a kernel bug? If yes, I think
-EFAULT is probably a weird error code to choose here. If no, this
should probably use WARN_ON(). Same thing in cetregs_set().
When a thread is not CET-enabled, its CET state does not exist. I
looked at EFAULT, and it means "Bad address". Maybe this can be ENODEV,
which means "No such device"?
[...]
@@ -1284,6 +1293,13 @@ static struct user_regset x86_32_regsets[] __ro_after_init = {
[...]
+ [REGSET_CET32] = {
+ .core_note_type = NT_X86_CET,
+ .n = sizeof(struct cet_user_state) / sizeof(u64),
+ .size = sizeof(u64), .align = sizeof(u64),
+ .active = cetregs_active, .regset_get = cetregs_get,
+ .set = cetregs_set
+ },
};
Why are there different identifiers for 32-bit CET and 64-bit CET when
they operate on the same structs and have the same handlers? If
there's a good reason for that, the commit message should probably
point that out.
Yes, the reason for two regsets is that fill_note_info() does not expect
any holes in a regsets. I will put this in the commit log.
Thanks,
Yu-cheng
