Re: [PATCH V2 1/3] riscv: Fixup static_obj() fail

From: Guo Ren
Date: Wed Oct 07 2020 - 10:45:44 EST

On Wed, Oct 7, 2020 at 4:39 AM Atish Patra <atishp@xxxxxxxxxxxxxx> wrote:
>
> On Tue, Oct 6, 2020 at 9:46 AM Guo Ren <guoren@xxxxxxxxxx> wrote:
> >
> > On Tue, Oct 6, 2020 at 3:14 AM Atish Patra <atishp@xxxxxxxxxxxxxx> wrote:
> > >
> > > On Thu, Sep 24, 2020 at 9:19 AM Guo Ren <guoren@xxxxxxxxxx> wrote:
> > > >
> > > > How about this, revert the commit and don't free INIT_DATA_SECTION. I
> > > > think the solution is safe enough, but wast a little memory.
> > > >
> > > > diff --git a/arch/riscv/kernel/vmlinux.lds.S b/arch/riscv/kernel/vmlinux.lds.S
> > > > index f3586e3..34d00d9 100644
> > > > --- a/arch/riscv/kernel/vmlinux.lds.S
> > > > +++ b/arch/riscv/kernel/vmlinux.lds.S
> > > > @@ -22,13 +22,11 @@ SECTIONS
> > > > /* Beginning of code and text segment */
> > > > . = LOAD_OFFSET;
> > > > _start = .;
> > > > - _stext = .;
> > > > HEAD_TEXT_SECTION
> > > > . = ALIGN(PAGE_SIZE);
> > > >
> > > > __init_begin = .;
> > > > INIT_TEXT_SECTION(PAGE_SIZE)
> > > > - INIT_DATA_SECTION(16)
> > > > . = ALIGN(8);
> > > > __soc_early_init_table : {
> > > > __soc_early_init_table_start = .;
> > > > @@ -55,6 +53,7 @@ SECTIONS
> > > > . = ALIGN(SECTION_ALIGN);
> > > > .text : {
> > > > _text = .;
> > > > + _stext = .;
> > > > TEXT_TEXT
> > > > SCHED_TEXT
> > > > CPUIDLE_TEXT
> > > > @@ -67,6 +66,8 @@ SECTIONS
> > > > _etext = .;
> > > > }
> > > >
> > > > + INIT_DATA_SECTION(16)
> > > > +
> > >
> > > I think you need to move EXIT_DATA as well. Currently, we have init
> > > data & text in one section.
> > It's not related to this issue. There is two check code problem:
>
> Yes. But we shouldn't move only INIT_DATA_SECTION out of __init section
> while leaving percpu & exit data in the __init section. Here is what I
> have in mind.
>
> diff --git a/arch/riscv/kernel/vmlinux.lds.S
> b/arch/riscv/kernel/vmlinux.lds.S
> index 9795359cb9da..4432cef8184e 100644
> --- a/arch/riscv/kernel/vmlinux.lds.S
> +++ b/arch/riscv/kernel/vmlinux.lds.S
> @@ -26,13 +26,11 @@ SECTIONS
> /* Beginning of code and text segment */
> . = LOAD_OFFSET;
> _start = .;
> _start = .;
> - _stext = .;
> HEAD_TEXT_SECTION
> . = ALIGN(PAGE_SIZE);
>
> __init_begin = .;
> INIT_TEXT_SECTION(PAGE_SIZE)
> - INIT_DATA_SECTION(16)
> . = ALIGN(8);
> __soc_early_init_table : {
> __soc_early_init_table_start = .;
> @@ -49,16 +47,13 @@ SECTIONS
> {
> EXIT_TEXT
> }
> - .exit.data :
> - {
> - EXIT_DATA
> - }
> - PERCPU_SECTION(L1_CACHE_BYTES)
> +
> __init_end = .;
>
> . = ALIGN(SECTION_ALIGN);
> .text : {
> _text = .;
> + _stext = .;
> TEXT_TEXT
> SCHED_TEXT
> CPUIDLE_TEXT
> @@ -77,6 +72,17 @@ SECTIONS
> #endif
>
> /* Start of data section */
> + __init_data_begin = .;
> + INIT_DATA_SECTION(16)
> + .exit.data :
> + {
> + EXIT_DATA
> + }
> +
> + PERCPU_SECTION(L1_CACHE_BYTES)
> +
> + __init_data_end = .;
> +
>
> As you correctly pointed out, this wastes around ~200K init memory
> that is wasted.
> That is not an ideal solution.
>
> The other alternative is to move __init_text section after _text as
> well similar to other architectures. But that won't work
> for RISC-V as we jump from _start to __start_kernel(in __init section)
> in head.S. A JAL instruction can't be fit because
> __start_kernel is now too far. We can't replace JAL with a JALR
> because that would require an additional
> instruction and violates image header format.
>
> Any other ideas to solve this problem without wasting memory ?
How about:

diff --git a/arch/riscv/include/asm/sections.h
b/arch/riscv/include/asm/sections.h
new file mode 100644
index 00000000..2317b9e
--- /dev/null
+++ b/arch/riscv/include/asm/sections.h
@@ -0,0 +1,20 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#ifndef _ASM_RISCV_SECTIONS_H
+#define _ASM_RISCV_SECTIONS_H
+
+#define arch_is_kernel_data arch_is_kernel_data
+
+#include <asm-generic/sections.h>
+
+extern bool init_mem_is_free;
+
+static inline int arch_is_kernel_data(unsigned long addr)
+{
+ if (init_mem_is_free)
+ return 0;
+
+ return addr >= (unsigned long)__init_begin &&
+ addr < (unsigned long)__init_end;
+}
+#endif /* _ASM_RISCV_SECTIONS_H */
diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c
index 2c6dd32..9ebd5eb4 100644
--- a/arch/riscv/kernel/setup.c
+++ b/arch/riscv/kernel/setup.c
@@ -17,6 +17,7 @@
#include <linux/sched/task.h>
#include <linux/swiotlb.h>
#include <linux/smp.h>
+#include <linux/poison.h>

#include <asm/cpu_ops.h>
#include <asm/setup.h>
@@ -112,3 +113,11 @@ static int __init topology_init(void)
return 0;
}
subsys_initcall(topology_init);
+
+bool init_mem_is_free = false;
+
+void free_initmem(void)
+{
+ free_initmem_default(POISON_FREE_INITMEM);
+ init_mem_is_free = true;
+}

>
> > 1. static int static_obj(const void *obj)
> > {
> > unsigned long start = (unsigned long) &_stext,
> > end = (unsigned long) &_end,
> > addr = (unsigned long) obj;
> >
> > /*
> > * static variable?
> > */
> > if ((addr >= start) && (addr < end))
> > return 1;
> >
> > 2. /* Is this address range in the kernel text area? */
> > static inline void check_kernel_text_object(const unsigned long ptr,
> > unsigned long n, bool to_user)
> > {
> > unsigned long textlow = (unsigned long)_stext;
> > unsigned long texthigh = (unsigned long)_etext;
> > unsigned long textlow_linear, texthigh_linear;
> >
> > if (overlaps(ptr, n, textlow, texthigh))
> > usercopy_abort("kernel text", NULL, to_user, ptr -
> > textlow, n);
> >
> > The patch of commit: a0fa4027dc911 (riscv: Fixup static_obj() fail) broke 2th.
> >
> > > In general it is better idea to separate those similar to ARM64.
> > > Additionally, ARM64 applies different mapping for init data & text
> > > as the init data section is marked as non-executable[1]
> > Yes, it's safer to protect init text & init data, but it's should be
> > another patch.
> >
>
> Yes. I will send the patch based on this fix.
>
> > >
> > > However, we don't modify any permission for any init sections. Should
> > > we do that as well ?
> > Agree, we should do that.
> >
> > >
> > > [1] https://patchwork.kernel.org/patch/9572869/
> > >
> > > > /* Start of data section */
> > > > _sdata = .;
> > > > RO_DATA(SECTION_ALIGN)
> > > >
> > > > On Thu, Sep 24, 2020 at 3:36 PM Andreas Schwab <schwab@xxxxxxxxxxxxxx> wrote:
> > > > >
> > > > > On Sep 14 2020, Aurelien Jarno wrote:
> > > > >
> > > > > > How should we proceed to get that fixed in time for 5.9? For the older
> > > > > > branches where it has been backported (so far 5.7 and 5.8), should we
> > > > > > just get that commit reverted instead?
> > > > >
> > > > > Can this please be resolved ASAP?
> > > > >
> > > > > Andreas.
> > > > >
> > > > > --
> > > > > Andreas Schwab, schwab@xxxxxxxxxxxxxx
> > > > > GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510 2552 DF73 E780 A9DA AEC1
> > > > > "And now for something completely different."
> > > >
> > > >
> > > >
> > > > --
> > > > Best Regards
> > > > Guo Ren
> > > >
> > > > ML: https://lore.kernel.org/linux-csky/
> > > >
> > > > _______________________________________________
> > > > linux-riscv mailing list
> > > > linux-riscv@xxxxxxxxxxxxxxxxxxx
> > > > http://lists.infradead.org/mailman/listinfo/linux-riscv
> > >
> > >
> > >
> > > --
> > > Regards,
> > > Atish
> >
> >
> >
> > --
> > Best Regards
> > Guo Ren
> >
> > ML: https://lore.kernel.org/linux-csky/
>
>
>
> --
> Regards,
> Atish



--
Best Regards
Guo Ren

ML: https://lore.kernel.org/linux-csky/