| Message ID | 20180514094640.27569-12-mark.rutland@arm.com |
|---|---|
| State | New |
| Headers | show |
| Series | arm64: invoke syscalls with pt_regs | expand |
On Mon, May 14, 2018 at 10:46:33AM +0100, Mark Rutland wrote: > We can zero GPRs x0 - x29 upon entry from EL0 to make it harder for > userspace to control values consumed by speculative gadgets. > > We don't blat x30, since this is stashed much later, and we'll blat it > before invoking C code. > > Signed-off-by: Mark Rutland <mark.rutland@arm.com> > Cc: Catalin Marinas <catalin.marinas@arm.com> > Cc: Will Deacon <will.deacon@arm.com> > --- > arch/arm64/kernel/entry.S | 9 +++++++-- > 1 file changed, 7 insertions(+), 2 deletions(-) > > diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S > index 13afefbf608f..4dd529fd03fd 100644 > --- a/arch/arm64/kernel/entry.S > +++ b/arch/arm64/kernel/entry.S > @@ -62,6 +62,12 @@ > #endif > .endm > > + .macro clear_gp_regs > + .irp n,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29 > + mov x\n, xzr > + .endr > + .endm > + Looks OK, but consider moving _for from fpsimdmacros.h to assembler.h and just writing _for n, 0, 29, mov x\n, xzr (could even omit the wrapper macro, since this is a one-liner). The implementation of _for is a bit gross, but since we already have it, we might as well use it. [...] Cheers ---Dave
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S index 13afefbf608f..4dd529fd03fd 100644 --- a/arch/arm64/kernel/entry.S +++ b/arch/arm64/kernel/entry.S @@ -62,6 +62,12 @@ #endif .endm + .macro clear_gp_regs + .irp n,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29 + mov x\n, xzr + .endr + .endm + /* * Bad Abort numbers *----------------- @@ -158,12 +164,11 @@ alternative_else_nop_endif stp x28, x29, [sp, #16 * 14] .if \el == 0 + clear_gp_regs mrs x21, sp_el0 ldr_this_cpu tsk, __entry_task, x20 // Ensure MDSCR_EL1.SS is clear, ldr x19, [tsk, #TSK_TI_FLAGS] // since we can unmask debug disable_step_tsk x19, x20 // exceptions when scheduling. - - mov x29, xzr // fp pointed to user-space .else add x21, sp, #S_FRAME_SIZE get_thread_info tsk
We can zero GPRs x0 - x29 upon entry from EL0 to make it harder for userspace to control values consumed by speculative gadgets. We don't blat x30, since this is stashed much later, and we'll blat it before invoking C code. Signed-off-by: Mark Rutland <mark.rutland@arm.com> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Will Deacon <will.deacon@arm.com> --- arch/arm64/kernel/entry.S | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) -- 2.11.0