| Message ID | 20220914154746.1122482-3-npiggin@gmail.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | powerpc: build / linker improvements | expand |
Le 14/09/2022 à 17:47, Nicholas Piggin a écrit : > powerpc has a number of read-only sections and tables that are put > after RO_DATA(). Move the __end_rodata symbol to cover these as well. > > Setting memory to read-only at boot is done using __init_begin, > change that that to use __end_rodata. I see the idea after looking in more details in the generated code, but I think this commit description needs to be more explanatory. In mm/pgtable_32.c there was a comment explaining why __init_begin is used. I think you need to explain why we don't want to use it anymore and why we can now use __end_rodata. > > This also affects boot dmesg, is_kernel_rodata(), and some other checks. > > Signed-off-by: Nicholas Piggin <npiggin@gmail.com> > --- > arch/powerpc/kernel/vmlinux.lds.S | 3 +++ > arch/powerpc/mm/book3s32/mmu.c | 2 +- > arch/powerpc/mm/book3s64/hash_pgtable.c | 2 +- > arch/powerpc/mm/book3s64/radix_pgtable.c | 2 +- > arch/powerpc/mm/pgtable_32.c | 5 ++--- > 5 files changed, 8 insertions(+), 6 deletions(-) > > diff --git a/arch/powerpc/kernel/vmlinux.lds.S b/arch/powerpc/kernel/vmlinux.lds.S > index fe22d940412f..90ac5ff73df2 100644 > --- a/arch/powerpc/kernel/vmlinux.lds.S > +++ b/arch/powerpc/kernel/vmlinux.lds.S > @@ -210,6 +210,9 @@ SECTIONS > } > #endif > > + . = ALIGN(PAGE_SIZE); > + __end_rodata = .; > + I think this will likely break block mapping on PPC32. It needs to be aligned to STRICT_ALIGN_SIZE, like __init_begin is. > /* > * Init sections discarded at runtime > */ > diff --git a/arch/powerpc/mm/book3s32/mmu.c b/arch/powerpc/mm/book3s32/mmu.c > index a96b73006dfb..e13b883e4e5b 100644 > --- a/arch/powerpc/mm/book3s32/mmu.c > +++ b/arch/powerpc/mm/book3s32/mmu.c > @@ -240,7 +240,7 @@ void mmu_mark_rodata_ro(void) > for (i = 0; i < nb; i++) { > struct ppc_bat *bat = BATS[i]; > > - if (bat_addrs[i].start < (unsigned long)__init_begin) > + if (bat_addrs[i].start < (unsigned long)__end_rodata) > bat[1].batl = (bat[1].batl & ~BPP_RW) | BPP_RX; > } > > diff --git a/arch/powerpc/mm/book3s64/hash_pgtable.c b/arch/powerpc/mm/book3s64/hash_pgtable.c > index ae008b9df0e6..28332001bd87 100644 > --- a/arch/powerpc/mm/book3s64/hash_pgtable.c > +++ b/arch/powerpc/mm/book3s64/hash_pgtable.c > @@ -541,7 +541,7 @@ void hash__mark_rodata_ro(void) > unsigned long start, end, pp; > > start = (unsigned long)_stext; > - end = (unsigned long)__init_begin; > + end = (unsigned long)__end_rodata; > > pp = htab_convert_pte_flags(pgprot_val(PAGE_KERNEL_ROX), HPTE_USE_KERNEL_KEY); > > diff --git a/arch/powerpc/mm/book3s64/radix_pgtable.c b/arch/powerpc/mm/book3s64/radix_pgtable.c > index 698274109c91..2305f34bcc33 100644 > --- a/arch/powerpc/mm/book3s64/radix_pgtable.c > +++ b/arch/powerpc/mm/book3s64/radix_pgtable.c > @@ -228,7 +228,7 @@ void radix__mark_rodata_ro(void) > unsigned long start, end; > > start = (unsigned long)_stext; > - end = (unsigned long)__init_begin; > + end = (unsigned long)__end_rodata; > > radix__change_memory_range(start, end, _PAGE_WRITE); > } > diff --git a/arch/powerpc/mm/pgtable_32.c b/arch/powerpc/mm/pgtable_32.c > index 3ac73f9fb5d5..112af8c5447a 100644 > --- a/arch/powerpc/mm/pgtable_32.c > +++ b/arch/powerpc/mm/pgtable_32.c > @@ -158,10 +158,9 @@ void mark_rodata_ro(void) > } > > /* > - * mark .text and .rodata as read only. Use __init_begin rather than > - * __end_rodata to cover NOTES and EXCEPTION_TABLE. > + * mark .text and .rodata as read only. > */ > - numpages = PFN_UP((unsigned long)__init_begin) - > + numpages = PFN_UP((unsigned long)__end_rodata) - > PFN_DOWN((unsigned long)_stext); > > set_memory_ro((unsigned long)_stext, numpages);
Nicholas Piggin <npiggin@gmail.com> writes: > powerpc has a number of read-only sections and tables that are put > after RO_DATA(). Move the __end_rodata symbol to cover these as well. > > Setting memory to read-only at boot is done using __init_begin, > change that that to use __end_rodata. Did you just do that because it seems logical? Because it does seem logical, but it leaves a RWX region in the gap between __end_rodata and __init_begin, which is bad. This is the current behaviour, on radix: ---[ Start of kernel VM ]--- 0xc000000000000000-0xc000000001ffffff 0x0000000000000000 32M r X pte valid present dirty accessed 0xc000000002000000-0xc00000007fffffff 0x0000000002000000 2016M r w pte valid present dirty accessed And with your change: ---[ Start of kernel VM ]--- 0xc000000000000000-0xc0000000013fffff 0x0000000000000000 20M r X pte valid present dirty accessed 0xc000000001400000-0xc000000001ffffff 0x0000000001400000 12M r w X pte valid present dirty accessed 0xc000000002000000-0xc00000007fffffff 0x0000000002000000 2016M r w pte valid present dirty accessed On radix the 16M alignment is larger than we need, but we need to chose a value at build time that works for radix and hash. We could make the code smarter on radix, to mark those pages in between __end_rodata and __init_begin as RW_ and use them for data. But that would be a more involved change. I think if we just drop the changes to the C files this patch is OK to go in. cheers
On Thu Sep 15, 2022 at 10:47 PM AEST, Michael Ellerman wrote: > Nicholas Piggin <npiggin@gmail.com> writes: > > powerpc has a number of read-only sections and tables that are put > > after RO_DATA(). Move the __end_rodata symbol to cover these as well. > > > > Setting memory to read-only at boot is done using __init_begin, > > change that that to use __end_rodata. > > Did you just do that because it seems logical? I actually was looking at moving init so runtime code and data is closer. > Because it does seem logical, but it leaves a RWX region in the gap > between __end_rodata and __init_begin, which is bad. > > This is the current behaviour, on radix: > > ---[ Start of kernel VM ]--- > 0xc000000000000000-0xc000000001ffffff 0x0000000000000000 32M r X pte valid present dirty accessed > 0xc000000002000000-0xc00000007fffffff 0x0000000002000000 2016M r w pte valid present dirty accessed > > And with your change: > > ---[ Start of kernel VM ]--- > 0xc000000000000000-0xc0000000013fffff 0x0000000000000000 20M r X pte valid present dirty accessed > 0xc000000001400000-0xc000000001ffffff 0x0000000001400000 12M r w X pte valid present dirty accessed > 0xc000000002000000-0xc00000007fffffff 0x0000000002000000 2016M r w pte valid present dirty accessed > > > On radix the 16M alignment is larger than we need, but we need to chose > a value at build time that works for radix and hash. > > We could make the code smarter on radix, to mark those pages in between > __end_rodata and __init_begin as RW_ and use them for data. But that > would be a more involved change. Ah, yes Christophe pointed out it's broken too. We could just align __end_rodata to STRICT_ALIGN_SIZE for this patch? Thanks, Nick
"Nicholas Piggin" <npiggin@gmail.com> writes: > On Thu Sep 15, 2022 at 10:47 PM AEST, Michael Ellerman wrote: >> Nicholas Piggin <npiggin@gmail.com> writes: >> > powerpc has a number of read-only sections and tables that are put >> > after RO_DATA(). Move the __end_rodata symbol to cover these as well. >> > >> > Setting memory to read-only at boot is done using __init_begin, >> > change that that to use __end_rodata. >> >> Did you just do that because it seems logical? > > I actually was looking at moving init so runtime code and data is > closer. > >> Because it does seem logical, but it leaves a RWX region in the gap >> between __end_rodata and __init_begin, which is bad. >> >> This is the current behaviour, on radix: >> >> ---[ Start of kernel VM ]--- >> 0xc000000000000000-0xc000000001ffffff 0x0000000000000000 32M r X pte valid present dirty accessed >> 0xc000000002000000-0xc00000007fffffff 0x0000000002000000 2016M r w pte valid present dirty accessed >> >> And with your change: >> >> ---[ Start of kernel VM ]--- >> 0xc000000000000000-0xc0000000013fffff 0x0000000000000000 20M r X pte valid present dirty accessed >> 0xc000000001400000-0xc000000001ffffff 0x0000000001400000 12M r w X pte valid present dirty accessed >> 0xc000000002000000-0xc00000007fffffff 0x0000000002000000 2016M r w pte valid present dirty accessed >> >> >> On radix the 16M alignment is larger than we need, but we need to chose >> a value at build time that works for radix and hash. >> >> We could make the code smarter on radix, to mark those pages in between >> __end_rodata and __init_begin as RW_ and use them for data. But that >> would be a more involved change. > > Ah, yes Christophe pointed out it's broken too. We could just align > __end_rodata to STRICT_ALIGN_SIZE for this patch? Yeah that should work. I'd be happier if we had something more explicit to document that boundary, I'll send a patch. cheers
diff --git a/arch/powerpc/kernel/vmlinux.lds.S b/arch/powerpc/kernel/vmlinux.lds.S index fe22d940412f..90ac5ff73df2 100644 --- a/arch/powerpc/kernel/vmlinux.lds.S +++ b/arch/powerpc/kernel/vmlinux.lds.S @@ -210,6 +210,9 @@ SECTIONS } #endif + . = ALIGN(PAGE_SIZE); + __end_rodata = .; + /* * Init sections discarded at runtime */ diff --git a/arch/powerpc/mm/book3s32/mmu.c b/arch/powerpc/mm/book3s32/mmu.c index a96b73006dfb..e13b883e4e5b 100644 --- a/arch/powerpc/mm/book3s32/mmu.c +++ b/arch/powerpc/mm/book3s32/mmu.c @@ -240,7 +240,7 @@ void mmu_mark_rodata_ro(void) for (i = 0; i < nb; i++) { struct ppc_bat *bat = BATS[i]; - if (bat_addrs[i].start < (unsigned long)__init_begin) + if (bat_addrs[i].start < (unsigned long)__end_rodata) bat[1].batl = (bat[1].batl & ~BPP_RW) | BPP_RX; } diff --git a/arch/powerpc/mm/book3s64/hash_pgtable.c b/arch/powerpc/mm/book3s64/hash_pgtable.c index ae008b9df0e6..28332001bd87 100644 --- a/arch/powerpc/mm/book3s64/hash_pgtable.c +++ b/arch/powerpc/mm/book3s64/hash_pgtable.c @@ -541,7 +541,7 @@ void hash__mark_rodata_ro(void) unsigned long start, end, pp; start = (unsigned long)_stext; - end = (unsigned long)__init_begin; + end = (unsigned long)__end_rodata; pp = htab_convert_pte_flags(pgprot_val(PAGE_KERNEL_ROX), HPTE_USE_KERNEL_KEY); diff --git a/arch/powerpc/mm/book3s64/radix_pgtable.c b/arch/powerpc/mm/book3s64/radix_pgtable.c index 698274109c91..2305f34bcc33 100644 --- a/arch/powerpc/mm/book3s64/radix_pgtable.c +++ b/arch/powerpc/mm/book3s64/radix_pgtable.c @@ -228,7 +228,7 @@ void radix__mark_rodata_ro(void) unsigned long start, end; start = (unsigned long)_stext; - end = (unsigned long)__init_begin; + end = (unsigned long)__end_rodata; radix__change_memory_range(start, end, _PAGE_WRITE); } diff --git a/arch/powerpc/mm/pgtable_32.c b/arch/powerpc/mm/pgtable_32.c index 3ac73f9fb5d5..112af8c5447a 100644 --- a/arch/powerpc/mm/pgtable_32.c +++ b/arch/powerpc/mm/pgtable_32.c @@ -158,10 +158,9 @@ void mark_rodata_ro(void) } /* - * mark .text and .rodata as read only. Use __init_begin rather than - * __end_rodata to cover NOTES and EXCEPTION_TABLE. + * mark .text and .rodata as read only. */ - numpages = PFN_UP((unsigned long)__init_begin) - + numpages = PFN_UP((unsigned long)__end_rodata) - PFN_DOWN((unsigned long)_stext); set_memory_ro((unsigned long)_stext, numpages);
powerpc has a number of read-only sections and tables that are put after RO_DATA(). Move the __end_rodata symbol to cover these as well. Setting memory to read-only at boot is done using __init_begin, change that that to use __end_rodata. This also affects boot dmesg, is_kernel_rodata(), and some other checks. Signed-off-by: Nicholas Piggin <npiggin@gmail.com> --- arch/powerpc/kernel/vmlinux.lds.S | 3 +++ arch/powerpc/mm/book3s32/mmu.c | 2 +- arch/powerpc/mm/book3s64/hash_pgtable.c | 2 +- arch/powerpc/mm/book3s64/radix_pgtable.c | 2 +- arch/powerpc/mm/pgtable_32.c | 5 ++--- 5 files changed, 8 insertions(+), 6 deletions(-)