| Message ID | 1512059986-21325-14-git-send-email-will.deacon@arm.com |
|---|---|
| State | Superseded |
| Headers | show |
| Series | arm64: Unmap the kernel whilst running in userspace (KAISER) | expand |
On Thu, Nov 30, 2017 at 04:39:41PM +0000, Will Deacon wrote: > .macro kernel_ventry, el, label, regsize = 64 > .align 7 > +#ifdef CONFIG_UNMAP_KERNEL_AT_EL0 > + .if \el == 0 > + .if \regsize == 64 > + mrs x30, tpidrro_el0 > + msr tpidrro_el0, xzr > + .else > + mov x30, xzr I guess that's just to prevent acccidental leaks if we dump registers somewhere, since we used x30 as a scratch register? > + .macro tramp_alias, dst, sym > + mov_q \dst, TRAMP_VALIAS > + add \dst, \dst, #(\sym - .entry.tramp.text) > + .endm I didn't realise you could refer to sections like this; neat! Otherwise, looks fine to me. Thanks, Mark.
On Fri, Dec 01, 2017 at 01:53:01PM +0000, Mark Rutland wrote: > On Thu, Nov 30, 2017 at 04:39:41PM +0000, Will Deacon wrote: > > .macro kernel_ventry, el, label, regsize = 64 > > .align 7 > > +#ifdef CONFIG_UNMAP_KERNEL_AT_EL0 > > + .if \el == 0 > > + .if \regsize == 64 > > + mrs x30, tpidrro_el0 > > + msr tpidrro_el0, xzr > > + .else > > + mov x30, xzr > > I guess that's just to prevent acccidental leaks if we dump registers > somewhere, since we used x30 as a scratch register? Indeed. I don't have a concrete example, but I was worried about things like perf and ptrace, which might allow you to get at the AArch64 register state for a compat task so it felt like a good idea to zero this. Will
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S index 688e52f65a8d..99d105048663 100644 --- a/arch/arm64/kernel/entry.S +++ b/arch/arm64/kernel/entry.S @@ -73,6 +73,17 @@ .macro kernel_ventry, el, label, regsize = 64 .align 7 +#ifdef CONFIG_UNMAP_KERNEL_AT_EL0 + .if \el == 0 + .if \regsize == 64 + mrs x30, tpidrro_el0 + msr tpidrro_el0, xzr + .else + mov x30, xzr + .endif + .endif +#endif + sub sp, sp, #S_FRAME_SIZE #ifdef CONFIG_VMAP_STACK /* @@ -119,6 +130,11 @@ b el\()\el\()_\label .endm + .macro tramp_alias, dst, sym + mov_q \dst, TRAMP_VALIAS + add \dst, \dst, #(\sym - .entry.tramp.text) + .endm + .macro kernel_entry, el, regsize = 64 .if \regsize == 32 mov w0, w0 // zero upper 32 bits of x0 @@ -271,18 +287,20 @@ alternative_else_nop_endif .if \el == 0 ldr x23, [sp, #S_SP] // load return stack pointer msr sp_el0, x23 + tst x22, #PSR_MODE32_BIT // native task? + b.eq 3f + #ifdef CONFIG_ARM64_ERRATUM_845719 alternative_if ARM64_WORKAROUND_845719 - tbz x22, #4, 1f #ifdef CONFIG_PID_IN_CONTEXTIDR mrs x29, contextidr_el1 msr contextidr_el1, x29 #else msr contextidr_el1, xzr #endif -1: alternative_else_nop_endif #endif +3: .endif msr elr_el1, x21 // set up the return data @@ -304,7 +322,22 @@ alternative_else_nop_endif ldp x28, x29, [sp, #16 * 14] ldr lr, [sp, #S_LR] add sp, sp, #S_FRAME_SIZE // restore sp - eret // return to kernel + +#ifndef CONFIG_UNMAP_KERNEL_AT_EL0 + eret +#else + .if \el == 0 + bne 4f + msr far_el1, x30 + tramp_alias x30, tramp_exit_native + br x30 +4: + tramp_alias x30, tramp_exit_compat + br x30 + .else + eret + .endif +#endif .endm .macro irq_stack_entry
Hook up the entry trampoline to our exception vectors so that all exceptions from and returns to EL0 go via the trampoline, which swizzles the vector base register accordingly. Transitioning to and from the kernel clobbers x30, so we use tpidrro_el0 and far_el1 as scratch registers for native tasks. Signed-off-by: Will Deacon <will.deacon@arm.com> --- arch/arm64/kernel/entry.S | 39 ++++++++++++++++++++++++++++++++++++--- 1 file changed, 36 insertions(+), 3 deletions(-) -- 2.1.4