Re: [PATCH v11 6/9] x86/cet: Add PTRACE interface for CET

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



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




[Index of Archives]     [Linux ARM Kernel]     [Linux ARM]     [Linux Omap]     [Fedora ARM]     [IETF Annouce]     [Bugtraq]     [Linux OMAP]     [Linux MIPS]     [eCos]     [Asterisk Internet PBX]     [Linux API]

  Powered by Linux