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().
> + return membuf_write(&to, cetregs, sizeof(struct cet_user_state));
> +}
[...]
> diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c
[...]
> @@ -52,7 +52,9 @@ enum x86_regset {
> REGSET_IOPERM64 = REGSET_XFP,
> REGSET_XSTATE,
> REGSET_TLS,
> + REGSET_CET64 = REGSET_TLS,
> REGSET_IOPERM32,
> + REGSET_CET32,
> };
[...]
> @@ -1229,6 +1231,13 @@ static struct user_regset x86_64_regsets[] __ro_after_init = {
[...]
> + [REGSET_CET64] = {
> + .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
> + },
> };
[...]
> @@ -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.
