Re: [PATCH v2] riscv: Map the kernel with correct permissions the first time

Drew Fustini
2021-05-29T17:48:53Z

On Fri, May 28, 2021 at 09:08:43PM -0700, Drew Fustini wrote:
> On Wed, May 26, 2021 at 03:41:10PM +0200, Alexandre Ghiti wrote:
> > For 64b kernels, we map all the kernel with write and execute permissions
> > and afterwards remove writability from text and executability from data.
> >
> > For 32b kernels, the kernel mapping resides in the linear mapping, so we
> > map all the linear mapping as writable and executable and afterwards we
> > remove those properties for unused memory and kernel mapping as
> > described above.
> >
> > Change this behavior to directly map the kernel with correct permissions
> > and avoid going through the whole mapping to fix the permissions.
> >
> > At the same time, this fixes an issue introduced by commit 2bfc6cd81bd1
> > ("riscv: Move kernel mapping outside of linear mapping") as reported
> > here https://github.com/starfive-tech/linux/issues/17.
> >
> > Signed-off-by: Alexandre Ghiti <alex@ghiti.fr>
> > ---
> >
> > Changes in v2:
> > * Rebased on top of for-next (and "riscv: mm: fix build errors caused by
> > mk_pmd()")
> > * Get rid of protect_kernel_linear_mapping_text_rodata as suggested by
> > Jisheng
> > * Improve code in general compared to previous RFC
> >
> > Tested on:
> >
> > * kernel
> > - rv32: OK
> > - rv64: OK
> >
> > * kernel w/o CONFIG_STRICT_KERNEL_RWX:
> > - rv32: OK
> > - rv64: OK
> >
> > * xipkernel:
> > - rv32: build only
> > - rv64: OK
> >
> > * nommukernel:
> > - rv64: build only
> >
> > arch/riscv/include/asm/page.h | 9 +-
> > arch/riscv/include/asm/sections.h | 16 ++++
> > arch/riscv/include/asm/set_memory.h | 8 --
> > arch/riscv/kernel/setup.c | 5 --
> > arch/riscv/mm/init.c | 123 +++++++++++++++-------------
> > 5 files changed, 89 insertions(+), 72 deletions(-)
> >
> > diff --git a/arch/riscv/include/asm/page.h b/arch/riscv/include/asm/page.h
> > index 6e004d8fda4d..7ff5e0d81e41 100644
> > --- a/arch/riscv/include/asm/page.h
> > +++ b/arch/riscv/include/asm/page.h
> > @@ -95,6 +95,7 @@ extern unsigned long va_kernel_pa_offset;
> > #endif
> > extern unsigned long va_kernel_xip_pa_offset;
> > extern unsigned long pfn_base;
> > +extern uintptr_t load_sz;
> > #define ARCH_PFN_OFFSET (pfn_base)
> > #else
> > #define va_pa_offset 0
> > @@ -108,6 +109,9 @@ extern unsigned long pfn_base;
> > extern unsigned long kernel_virt_addr;
> >
> > #ifdef CONFIG_64BIT
> > +#define is_kernel_mapping(x) ((x) >= kernel_virt_addr && (x) < (kernel_virt_addr + load_sz))
> > +#define is_linear_mapping(x) ((x) >= PAGE_OFFSET && (x) < kernel_virt_addr)
> > +
> > #define linear_mapping_pa_to_va(x) ((void *)((unsigned long)(x) + va_pa_offset))
> > #define kernel_mapping_pa_to_va(y) ({ \
> > unsigned long _y = y; \
> > @@ -127,10 +131,13 @@ extern unsigned long kernel_virt_addr;
> >
> > #define __va_to_pa_nodebug(x) ({ \
> > unsigned long _x = x; \
> > - (_x < kernel_virt_addr) ? \
> > + is_linear_mapping(_x) ? \
> > linear_mapping_va_to_pa(_x) : kernel_mapping_va_to_pa(_x); \
> > })
> > #else
> > +#define is_kernel_mapping(x) ((x) >= kernel_virt_addr && (x) < (kernel_virt_addr + load_sz))
> > +#define is_linear_mapping(x) ((x) >= PAGE_OFFSET)
> > +
> > #define __pa_to_va_nodebug(x) ((void *)((unsigned long) (x) + va_pa_offset))
> > #define __va_to_pa_nodebug(x) ((unsigned long)(x) - va_pa_offset)
> > #endif /* CONFIG_64BIT */
> > diff --git a/arch/riscv/include/asm/sections.h b/arch/riscv/include/asm/sections.h
> > index 8a303fb1ee3b..6b5affecca83 100644
> > --- a/arch/riscv/include/asm/sections.h
> > +++ b/arch/riscv/include/asm/sections.h
> > @@ -6,6 +6,7 @@
> > #define __ASM_SECTIONS_H
> >
> > #include <asm-generic/sections.h>
> > +#include <linux/mm.h>
> >
> > extern char _start[];
> > extern char _start_kernel[];
> > @@ -13,4 +14,19 @@ extern char __init_data_begin[], __init_data_end[];
> > extern char __init_text_begin[], __init_text_end[];
> > extern char __alt_start[], __alt_end[];
> >
> > +static inline bool is_va_kernel_text(uintptr_t va)
> > +{
> > + return (va >= (uintptr_t)_start && va < (uintptr_t)__init_text_begin);
> > +}
> > +
> > +static inline bool is_va_kernel_lm_alias_text(uintptr_t va)
> > +{
> > + return (va >= (uintptr_t)lm_alias(_start) && va < (uintptr_t)lm_alias(__init_text_begin));
> > +}
> > +
> > +static inline bool is_va_kernel_init_text(uintptr_t va)
> > +{
> > + return (va >= (uintptr_t)__init_text_begin && va < (uintptr_t)__init_data_begin);
> > +}
> > +
> > #endif /* __ASM_SECTIONS_H */
> > diff --git a/arch/riscv/include/asm/set_memory.h b/arch/riscv/include/asm/set_memory.h
> > index 086f757e8ba3..ebb8516ec5bc 100644
> > --- a/arch/riscv/include/asm/set_memory.h
> > +++ b/arch/riscv/include/asm/set_memory.h
> > @@ -16,22 +16,14 @@ int set_memory_rw(unsigned long addr, int numpages);
> > int set_memory_x(unsigned long addr, int numpages);
> > int set_memory_nx(unsigned long addr, int numpages);
> > int set_memory_rw_nx(unsigned long addr, int numpages);
> > -void protect_kernel_text_data(void);
> > #else
> > static inline int set_memory_ro(unsigned long addr, int numpages) { return 0; }
> > static inline int set_memory_rw(unsigned long addr, int numpages) { return 0; }
> > static inline int set_memory_x(unsigned long addr, int numpages) { return 0; }
> > static inline int set_memory_nx(unsigned long addr, int numpages) { return 0; }
> > -static inline void protect_kernel_text_data(void) {}
> > static inline int set_memory_rw_nx(unsigned long addr, int numpages) { return 0; }
> > #endif
> >
> > -#if defined(CONFIG_64BIT) && defined(CONFIG_STRICT_KERNEL_RWX)
> > -void protect_kernel_linear_mapping_text_rodata(void);
> > -#else
> > -static inline void protect_kernel_linear_mapping_text_rodata(void) {}
> > -#endif
> > -
> > int set_direct_map_invalid_noflush(struct page *page);
> > int set_direct_map_default_noflush(struct page *page);
> > bool kernel_page_present(struct page *page);
> > diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c
> > index 4db4d0b5911f..96f483e7c279 100644
> > --- a/arch/riscv/kernel/setup.c
> > +++ b/arch/riscv/kernel/setup.c
> > @@ -290,11 +290,6 @@ void __init setup_arch(char **cmdline_p)
> > init_resources();
> > sbi_init();
> >
> > - if (IS_ENABLED(CONFIG_STRICT_KERNEL_RWX)) {
> > - protect_kernel_text_data();
> > - protect_kernel_linear_mapping_text_rodata();
> > - }
> > -
> > #ifdef CONFIG_SWIOTLB
> > swiotlb_init(1);
> > #endif
> > diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> > index 2d80088f33d5..4b1bcbbd50aa 100644
> > --- a/arch/riscv/mm/init.c
> > +++ b/arch/riscv/mm/init.c
> > @@ -425,6 +425,63 @@ asmlinkage void __init __copy_data(void)
> > }
> > #endif
> >
> > +#ifdef CONFIG_STRICT_KERNEL_RWX
> > +static __init pgprot_t pgprot_from_va(uintptr_t va)
> > +{
> > +#ifdef CONFIG_64BIT
> > + if (is_va_kernel_text(va) || is_va_kernel_init_text(va))
> > + return PAGE_KERNEL_READ_EXEC;
> > +
> > + /*
> > + * We must mark only text as read-only as init text will get freed later
> > + * and rodata section is marked readonly in mark_rodata_ro.
> > + */
> > + if (is_va_kernel_lm_alias_text(va))
> > + return PAGE_KERNEL_READ;
> > +
> > + return PAGE_KERNEL;
> > +#else
> > + if (is_va_kernel_text(va))
> > + return PAGE_KERNEL_READ_EXEC;
> > +
> > + if (is_va_kernel_init_text(va))
> > + return PAGE_KERNEL_EXEC;
> > +
> > + return PAGE_KERNEL;
> > +#endif /* CONFIG_64BIT */
> > +}
> > +
> > +void mark_rodata_ro(void)
> > +{
> > + unsigned long rodata_start = (unsigned long)__start_rodata;
> > + unsigned long data_start = (unsigned long)_data;
> > + unsigned long __maybe_unused lm_rodata_start = (unsigned long)lm_alias(__start_rodata);
> > + unsigned long __maybe_unused lm_data_start = (unsigned long)lm_alias(_data);
> > +
> > + set_memory_ro(rodata_start, (data_start - rodata_start) >> PAGE_SHIFT);
> > +#ifdef CONFIG_64BIT
> > + set_memory_ro(lm_rodata_start, (lm_data_start - lm_rodata_start) >> PAGE_SHIFT);
> > +#endif
> > +
> > + debug_checkwx();
> > +}
> > +#else /* CONFIG_STRICT_KERNEL_RWX */
> > +static __init pgprot_t pgprot_from_va(uintptr_t va)
> > +{
> > +#ifdef CONFIG_64BIT
> > + if (is_kernel_mapping(va))
> > + return PAGE_KERNEL_EXEC;
> > +
> > + if (is_linear_mapping(va))
> > + return PAGE_KERNEL;
> > +
> > + return PAGE_KERNEL;
> > +#else
> > + return PAGE_KERNEL_EXEC;
> > +#endif /* CONFIG_64BIT */
> > +}
> > +#endif /* CONFIG_STRICT_KERNEL_RWX */
> > +
> > /*
> > * setup_vm() is called from head.S with MMU-off.
> > *
> > @@ -454,7 +511,8 @@ uintptr_t xiprom, xiprom_sz;
> > #define xiprom_sz (*((uintptr_t *)XIP_FIXUP(&xiprom_sz)))
> > #define xiprom (*((uintptr_t *)XIP_FIXUP(&xiprom)))
> >
> > -static void __init create_kernel_page_table(pgd_t *pgdir, uintptr_t map_size)
> > +static void __init create_kernel_page_table(pgd_t *pgdir, uintptr_t map_size,
> > + __always_unused bool early)
> > {
> > uintptr_t va, end_va;
> >
> > @@ -473,7 +531,7 @@ static void __init create_kernel_page_table(pgd_t *pgdir, uintptr_t map_size)
> > map_size, PAGE_KERNEL);
> > }
> > #else
> > -static void __init create_kernel_page_table(pgd_t *pgdir, uintptr_t map_size)
> > +static void __init create_kernel_page_table(pgd_t *pgdir, uintptr_t map_size, bool early)
> > {
> > uintptr_t va, end_va;
> >
> > @@ -481,7 +539,7 @@ static void __init create_kernel_page_table(pgd_t *pgdir, uintptr_t map_size)
> > for (va = kernel_virt_addr; va < end_va; va += map_size)
> > create_pgd_mapping(pgdir, va,
> > load_pa + (va - kernel_virt_addr),
> > - map_size, PAGE_KERNEL_EXEC);
> > + map_size, early ? PAGE_KERNEL_EXEC : pgprot_from_va(va));
> > }
> > #endif
> >
> > @@ -558,7 +616,7 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
> > * us to reach paging_init(). We map all memory banks later
> > * in setup_vm_final() below.
> > */
> > - create_kernel_page_table(early_pg_dir, map_size);
> > + create_kernel_page_table(early_pg_dir, map_size, true);
> >
> > #ifndef __PAGETABLE_PMD_FOLDED
> > /* Setup early PMD for DTB */
> > @@ -634,22 +692,6 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
> > #endif
> > }
> >
> > -#if defined(CONFIG_64BIT) && defined(CONFIG_STRICT_KERNEL_RWX)
> > -void protect_kernel_linear_mapping_text_rodata(void)
> > -{
> > - unsigned long text_start = (unsigned long)lm_alias(_start);
> > - unsigned long init_text_start = (unsigned long)lm_alias(__init_text_begin);
> > - unsigned long rodata_start = (unsigned long)lm_alias(__start_rodata);
> > - unsigned long data_start = (unsigned long)lm_alias(_data);
> > -
> > - set_memory_ro(text_start, (init_text_start - text_start) >> PAGE_SHIFT);
> > - set_memory_nx(text_start, (init_text_start - text_start) >> PAGE_SHIFT);
> > -
> > - set_memory_ro(rodata_start, (data_start - rodata_start) >> PAGE_SHIFT);
> > - set_memory_nx(rodata_start, (data_start - rodata_start) >> PAGE_SHIFT);
> > -}
> > -#endif
> > -
> > static void __init setup_vm_final(void)
> > {
> > uintptr_t va, map_size;
> > @@ -682,21 +724,15 @@ static void __init setup_vm_final(void)
> > map_size = best_map_size(start, end - start);
> > for (pa = start; pa < end; pa += map_size) {
> > va = (uintptr_t)__va(pa);
> > - create_pgd_mapping(swapper_pg_dir, va, pa,
> > - map_size,
> > -#ifdef CONFIG_64BIT
> > - PAGE_KERNEL
> > -#else
> > - PAGE_KERNEL_EXEC
> > -#endif
> > - );
> >
> > + create_pgd_mapping(swapper_pg_dir, va, pa, map_size,
> > + pgprot_from_va(va));
> > }
> > }
> >
> > #ifdef CONFIG_64BIT
> > /* Map the kernel */
> > - create_kernel_page_table(swapper_pg_dir, PMD_SIZE);
> > + create_kernel_page_table(swapper_pg_dir, PMD_SIZE, false);
> > #endif
> >
> > /* Clear fixmap PTE and PMD mappings */
> > @@ -727,35 +763,6 @@ static inline void setup_vm_final(void)
> > }
> > #endif /* CONFIG_MMU */
> >
> > -#ifdef CONFIG_STRICT_KERNEL_RWX
> > -void __init protect_kernel_text_data(void)
> > -{
> > - unsigned long text_start = (unsigned long)_start;
> > - unsigned long init_text_start = (unsigned long)__init_text_begin;
> > - unsigned long init_data_start = (unsigned long)__init_data_begin;
> > - unsigned long rodata_start = (unsigned long)__start_rodata;
> > - unsigned long data_start = (unsigned long)_data;
> > - unsigned long max_low = (unsigned long)(__va(PFN_PHYS(max_low_pfn)));
> > -
> > - set_memory_ro(text_start, (init_text_start - text_start) >> PAGE_SHIFT);
> > - set_memory_ro(init_text_start, (init_data_start - init_text_start) >> PAGE_SHIFT);
> > - set_memory_nx(init_data_start, (rodata_start - init_data_start) >> PAGE_SHIFT);
> > - /* rodata section is marked readonly in mark_rodata_ro */
> > - set_memory_nx(rodata_start, (data_start - rodata_start) >> PAGE_SHIFT);
> > - set_memory_nx(data_start, (max_low - data_start) >> PAGE_SHIFT);
> > -}
> > -
> > -void mark_rodata_ro(void)
> > -{
> > - unsigned long rodata_start = (unsigned long)__start_rodata;
> > - unsigned long data_start = (unsigned long)_data;
> > -
> > - set_memory_ro(rodata_start, (data_start - rodata_start) >> PAGE_SHIFT);
> > -
> > - debug_checkwx();
> > -}
> > -#endif
> > -
> > #ifdef CONFIG_KEXEC_CORE
> > /*
> > * reserve_crashkernel() - reserves memory for crash kernel
> > --
> > 2.30.2
> >
> >
> > _______________________________________________
> > linux-riscv mailing list
> > linux-riscv@lists.infradead.org
> > http://lists.infradead.org/mailman/listinfo/linux-riscv
>
> I wanted to try testing this on the BeagleV Starlight but I could not
> apply it cleanly against 5.13-rc3:
>
> $ git am /tmp/patch.am
> Applying: riscv: Map the kernel with correct permissions the first time
> error: patch failed: arch/riscv/include/asm/page.h:95
> error: arch/riscv/include/asm/page.h: patch does not apply
> Patch failed at 0001 riscv: Map the kernel with correct permissions the first time
> hint: Use 'git am --show-current-patch=diff' to see the failed patch
> When you have resolved this problem, run "git am --continue".
> If you prefer to skip this patch, run "git am --skip" instead.
> To restore the original branch and stop patching, run "git am --abort".
>
> Is there another branch I should be looking at?
>
> thanks,
> drew

I realized I should have using riscv/for-next but I still seem to
encounter problem applying:

$ git checkout -b riscv_for_next riscv/for-next
Branch 'riscv_for_next' set up to track remote branch 'for-next' from 'riscv'.
Switched to a new branch 'riscv_for_next'
pdp7@x1:~/dev/starfive/linux$ git status
On branch riscv_for_next
Your branch is up to date with 'riscv/for-next'.

nothing to commit, working tree clean

$ git log -1 --oneline
37a7a2a10ec5 (HEAD -> riscv_for_next, riscv/for-next) riscv: Turn has_fpu into a static key if FPU=y

$ b4 am 20210526134110.217073-1-alex@ghiti.fr
Looking up https://lore.kernel.org/r/20210526134110.217073-1-alex%40ghiti.fr
Grabbing thread from lore.kernel.org/linux-riscv
Analyzing 4 messages in the thread
---
Writing ./v2_20210526_alex_riscv_map_the_kernel_with_correct_permissions_the_first_time.mbx
[PATCH v2] riscv: Map the kernel with correct permissions the first time
---
Total patches: 1
---
Link: https://lore.kernel.org/r/20210526134110.217073-1-alex@ghiti.fr
Base: not found
git am ./v2_20210526_alex_riscv_map_the_kernel_with_correct_permissions_the_first_time.mbx

$ git am v2_20210526_alex_riscv_map_the_kernel_with_correct_permissions_the_first_time.mbx
Applying: riscv: Map the kernel with correct permissions the first time
error: patch failed: arch/riscv/include/asm/page.h:95
error: arch/riscv/include/asm/page.h: patch does not apply
Patch failed at 0001 riscv: Map the kernel with correct permissions the first time
hint: Use 'git am --show-current-patch=diff' to see the failed patch
When you have resolved this problem, run "git am --continue".
If you prefer to skip this patch, run "git am --skip" instead.
To restore the original branch and stop patching, run "git am --abort".

Am I doing something wrong?

Thanks,
Drew