| Message ID | 20170903120757.14968-21-ard.biesheuvel@linaro.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Sun, 3 Sep 2017, Ard Biesheuvel wrote: > To prepare for adding support for KASLR, which relocates all absolute > symbol references at runtime after the caches have been enabled, > update the MMU switch code to avoid using absolute symbol references > where possible. This ensures these quantities are invariant under > runtime relocation. > > Cc: Russell King <linux@armlinux.org.uk> > Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> > --- > arch/arm/kernel/head-common.S | 39 ++++++++------------ > 1 file changed, 15 insertions(+), 24 deletions(-) > > diff --git a/arch/arm/kernel/head-common.S b/arch/arm/kernel/head-common.S > index 06035488130c..b74477507a12 100644 > --- a/arch/arm/kernel/head-common.S > +++ b/arch/arm/kernel/head-common.S > @@ -79,9 +79,10 @@ ENDPROC(__vet_atags) > */ > __INIT > __mmap_switched: > - adr r3, __mmap_switched_data > - > - ldmia r3!, {r4, r5, r6, r7} > + adr_l r4, __data_loc > + adr_l r5, _sdata > + adr_l r6, __bss_start > + adr_l r7, _end > cmp r4, r5 @ Copy data segment if needed > 1: cmpne r5, r6 > ldrne fp, [r4], #4 > @@ -93,9 +94,17 @@ __mmap_switched: > strcc fp, [r6],#4 > bcc 1b > > - ARM( ldmia r3, {r4, r5, r6, r7, sp}) > - THUMB( ldmia r3, {r4, r5, r6, r7} ) > - THUMB( ldr sp, [r3, #16] ) > + adr_l r3, init_thread_union + THREAD_START_SP > + mov sp, r3 > + adr_l r4, processor_id > + adr_l r5, __machine_arch_type > + adr_l r6, __atags_pointer > +#ifdef CONFIG_CPU_CP15 > + adr_l r7, cr_alignment > +#else > + mov r7, #0 > +#endif The code that follows is testing for a non-zero r7 value to store r0 so you could make that code conditional rather than loading 0 here. > + > str r9, [r4] @ Save processor ID > str r1, [r5] @ Save machine type > str r2, [r6] @ Save atags pointer > @@ -104,24 +113,6 @@ __mmap_switched: > b start_kernel > ENDPROC(__mmap_switched) > > - .align 2 > - .type __mmap_switched_data, %object > -__mmap_switched_data: > - .long __data_loc @ r4 > - .long _sdata @ r5 > - .long __bss_start @ r6 > - .long _end @ r7 > - .long processor_id @ r4 > - .long __machine_arch_type @ r5 > - .long __atags_pointer @ r6 > -#ifdef CONFIG_CPU_CP15 > - .long cr_alignment @ r7 > -#else > - .long 0 @ r7 > -#endif > - .long init_thread_union + THREAD_START_SP @ sp > - .size __mmap_switched_data, . - __mmap_switched_data > - > /* > * This provides a C-API version of __lookup_processor_type > */ > -- > 2.11.0 > >
On 4 September 2017 at 19:15, Nicolas Pitre <nicolas.pitre@linaro.org> wrote: > On Sun, 3 Sep 2017, Ard Biesheuvel wrote: > >> To prepare for adding support for KASLR, which relocates all absolute >> symbol references at runtime after the caches have been enabled, >> update the MMU switch code to avoid using absolute symbol references >> where possible. This ensures these quantities are invariant under >> runtime relocation. >> >> Cc: Russell King <linux@armlinux.org.uk> >> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> >> --- >> arch/arm/kernel/head-common.S | 39 ++++++++------------ >> 1 file changed, 15 insertions(+), 24 deletions(-) >> >> diff --git a/arch/arm/kernel/head-common.S b/arch/arm/kernel/head-common.S >> index 06035488130c..b74477507a12 100644 >> --- a/arch/arm/kernel/head-common.S >> +++ b/arch/arm/kernel/head-common.S >> @@ -79,9 +79,10 @@ ENDPROC(__vet_atags) >> */ >> __INIT >> __mmap_switched: >> - adr r3, __mmap_switched_data >> - >> - ldmia r3!, {r4, r5, r6, r7} >> + adr_l r4, __data_loc >> + adr_l r5, _sdata >> + adr_l r6, __bss_start >> + adr_l r7, _end >> cmp r4, r5 @ Copy data segment if needed >> 1: cmpne r5, r6 >> ldrne fp, [r4], #4 >> @@ -93,9 +94,17 @@ __mmap_switched: >> strcc fp, [r6],#4 >> bcc 1b >> >> - ARM( ldmia r3, {r4, r5, r6, r7, sp}) >> - THUMB( ldmia r3, {r4, r5, r6, r7} ) >> - THUMB( ldr sp, [r3, #16] ) >> + adr_l r3, init_thread_union + THREAD_START_SP >> + mov sp, r3 >> + adr_l r4, processor_id >> + adr_l r5, __machine_arch_type >> + adr_l r6, __atags_pointer >> +#ifdef CONFIG_CPU_CP15 >> + adr_l r7, cr_alignment >> +#else >> + mov r7, #0 >> +#endif > > The code that follows is testing for a non-zero r7 value to store r0 so > you could make that code conditional rather than loading 0 here. > OK, I will look into that.
diff --git a/arch/arm/kernel/head-common.S b/arch/arm/kernel/head-common.S index 06035488130c..b74477507a12 100644 --- a/arch/arm/kernel/head-common.S +++ b/arch/arm/kernel/head-common.S @@ -79,9 +79,10 @@ ENDPROC(__vet_atags) */ __INIT __mmap_switched: - adr r3, __mmap_switched_data - - ldmia r3!, {r4, r5, r6, r7} + adr_l r4, __data_loc + adr_l r5, _sdata + adr_l r6, __bss_start + adr_l r7, _end cmp r4, r5 @ Copy data segment if needed 1: cmpne r5, r6 ldrne fp, [r4], #4 @@ -93,9 +94,17 @@ __mmap_switched: strcc fp, [r6],#4 bcc 1b - ARM( ldmia r3, {r4, r5, r6, r7, sp}) - THUMB( ldmia r3, {r4, r5, r6, r7} ) - THUMB( ldr sp, [r3, #16] ) + adr_l r3, init_thread_union + THREAD_START_SP + mov sp, r3 + adr_l r4, processor_id + adr_l r5, __machine_arch_type + adr_l r6, __atags_pointer +#ifdef CONFIG_CPU_CP15 + adr_l r7, cr_alignment +#else + mov r7, #0 +#endif + str r9, [r4] @ Save processor ID str r1, [r5] @ Save machine type str r2, [r6] @ Save atags pointer @@ -104,24 +113,6 @@ __mmap_switched: b start_kernel ENDPROC(__mmap_switched) - .align 2 - .type __mmap_switched_data, %object -__mmap_switched_data: - .long __data_loc @ r4 - .long _sdata @ r5 - .long __bss_start @ r6 - .long _end @ r7 - .long processor_id @ r4 - .long __machine_arch_type @ r5 - .long __atags_pointer @ r6 -#ifdef CONFIG_CPU_CP15 - .long cr_alignment @ r7 -#else - .long 0 @ r7 -#endif - .long init_thread_union + THREAD_START_SP @ sp - .size __mmap_switched_data, . - __mmap_switched_data - /* * This provides a C-API version of __lookup_processor_type */
To prepare for adding support for KASLR, which relocates all absolute symbol references at runtime after the caches have been enabled, update the MMU switch code to avoid using absolute symbol references where possible. This ensures these quantities are invariant under runtime relocation. Cc: Russell King <linux@armlinux.org.uk> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> --- arch/arm/kernel/head-common.S | 39 ++++++++------------ 1 file changed, 15 insertions(+), 24 deletions(-)