| Message ID | 20191031164637.48901-15-samitolvanen@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v3,01/17] arm64: mm: avoid x18 in idmap_kpti_install_ng_mappings | expand |
On Thu, Oct 31, 2019 at 09:46:34AM -0700, samitolvanen@google.com wrote: > If we detect a corrupted x18 and SCS is enabled, restore the register > before jumping back to instrumented code. This is safe, because the > wrapper is called with preemption disabled and a separate shadow stack > is used for interrupt handling. > > Signed-off-by: Sami Tolvanen <samitolvanen@google.com> Reviewed-by: Kees Cook <keescook@chromium.org> -Kees > --- > arch/arm64/kernel/efi-rt-wrapper.S | 7 ++++++- > 1 file changed, 6 insertions(+), 1 deletion(-) > > diff --git a/arch/arm64/kernel/efi-rt-wrapper.S b/arch/arm64/kernel/efi-rt-wrapper.S > index 3fc71106cb2b..945744f16086 100644 > --- a/arch/arm64/kernel/efi-rt-wrapper.S > +++ b/arch/arm64/kernel/efi-rt-wrapper.S > @@ -34,5 +34,10 @@ ENTRY(__efi_rt_asm_wrapper) > ldp x29, x30, [sp], #32 > b.ne 0f > ret > -0: b efi_handle_corrupted_x18 // tail call > +0: > +#ifdef CONFIG_SHADOW_CALL_STACK > + /* Restore x18 before returning to instrumented code. */ > + mov x18, x2 > +#endif > + b efi_handle_corrupted_x18 // tail call > ENDPROC(__efi_rt_asm_wrapper) > -- > 2.24.0.rc0.303.g954a862665-goog >
diff --git a/arch/arm64/kernel/efi-rt-wrapper.S b/arch/arm64/kernel/efi-rt-wrapper.S index 3fc71106cb2b..945744f16086 100644 --- a/arch/arm64/kernel/efi-rt-wrapper.S +++ b/arch/arm64/kernel/efi-rt-wrapper.S @@ -34,5 +34,10 @@ ENTRY(__efi_rt_asm_wrapper) ldp x29, x30, [sp], #32 b.ne 0f ret -0: b efi_handle_corrupted_x18 // tail call +0: +#ifdef CONFIG_SHADOW_CALL_STACK + /* Restore x18 before returning to instrumented code. */ + mov x18, x2 +#endif + b efi_handle_corrupted_x18 // tail call ENDPROC(__efi_rt_asm_wrapper)
If we detect a corrupted x18 and SCS is enabled, restore the register before jumping back to instrumented code. This is safe, because the wrapper is called with preemption disabled and a separate shadow stack is used for interrupt handling. Signed-off-by: Sami Tolvanen <samitolvanen@google.com> --- arch/arm64/kernel/efi-rt-wrapper.S | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-)