Re: [PATCH] riscv: mm: Synchronize memory attributes for all mm in free_initmem() on RV32 platform.

CL Wang
2023-10-18T02:56:46Z

Hi Alexandre,

First of all, thank you for your response.
You are right, this patch is a reference to the modification of the ARM platform
(08925c2f12, ARM: 8464/1: Update all mm structures with section adjustments), so
the modification will be very similar to the patch you mentioned.

However, it cannot be denied that in the RV32 environment, it is effortless to encounter
the memory attribute modification problem at boot time, and it is 100% reproducible. This
problem is still not fixed in the new version of the kernel.

So could you please advise me on whether I should continue refining this patch?

Thanks for your advice.

Best regards
CL

On Fri, Sep 29, 2023 at 12:43:48PM +0200, Alexandre Ghiti wrote:
> Hi CL,
>
>
> On Tue, Sep 12, 2023 at 11:34 AM CL Wang <cl634@andestech.com> wrote:
> >
> > 1. Symptom:
> > [ 44.486537] Unable to handle kernel paging request at virtual address c0800000
> > [ 44.509980] Oops [#1]
> > [ 44.516975] Modules linked in:
> > [ 44.526260] CPU: 0 PID: 1 Comm: swapper Not tainted 6.1.27-05153-g45f6a9286550-dirty #19
> > [ 44.550422] Hardware name: andestech,a45 (DT)
> > [ 44.563473] epc : __memset+0x58/0xf4
> > [ 44.574353] ra : free_reserved_area+0xb0/0x1a4
> > [ 44.588144] epc : c05d4ca0 ra : c011f32c sp : c2c61f00
> > [ 44.603536] gp : c28a57c8 tp : c2c98000 t0 : c0800000
> > [ 44.618916] t1 : 07901b48 t2 : 0000000f s0 : c2c61f50
> > [ 44.634308] s1 : 00000001 a0 : c0800000 a1 : cccccccc
> > [ 44.649696] a2 : 00001000 a3 : c0801000 a4 : 00000000
> > [ 44.665085] a5 : 02000000 a6 : c0800fff a7 : 00000c08
> > [ 44.680467] s2 : 000000cc s3 : ffffffff s4 : 00000000
> > [ 44.695846] s5 : c28a66cc s6 : c1eba000 s7 : c2125820
> > [ 44.711225] s8 : c0800000 s9 : c212583c s10: c28a6648
> > [ 44.726623] s11: fe03c7c0 t3 : acf917bf t4 : e0000000
> > [ 44.742009] t5 : c2ca0011 t6 : c2ca0016
> > [ 44.753789] status: 00000120 badaddr: c0800000 cause: 0000000f
> > [ 44.771234] [<c05d4ca0>] __memset+0x58/0xf4
> > [ 44.783895] [<c0003e54>] free_initmem+0x80/0x88
> > [ 44.797599] [<c05dcd5c>] kernel_init+0x3c/0x124
> > [ 44.811391] [<c0003428>] ret_from_exception+0x0/0x16
> >
> > 2. To reproduce the problem:
> > a. Use the RV32 toolchain to build the system.
> > b. Build in the SPI module and mtdpart module in the kernel
> > Example: Enable the following configuration
> > - CONFIG_SPI
> > - CONFIG_MTD and CONFIG_MTD_SPI_NOR
> > c. Enable the "Make kernel text and rodata read-only" option by using the
> > following kernel config.
> > - CONFIG_STRICT_KERNEL_RWX
> >
> > 3. Root cause:
> > This problem occurs when the virtual address of the kernel paging request
> > is mapped to a megapage on the RV32 platform.
> > During system startup, free_initmem() calls set_kernel_memory() to
> > change the memory attributes of the init section from RO to RW. It
> > then calls free_initmem_default() to set the memory to
> > POISON_FREE_INITMEM. If the system runs modprobe at boot time, it
> > will trigger a fork/exec to create a new mm for the new process. If
> > the modprobe was called before free_initmem(), it will cause a kernel
> > oops because the memory attributes of the current mm were not changed
> > by set_kernel_memory(). This is because the set_kernel_memory() changes
> > the memory attributes of init_mm, but the pgd(satp) currently in use
> > is another process's mm and it's memory attribute doesn't change.
> > Thus, it causes a kernel oops because the memory region has an
> > un-writable attribute.
> >
> > 4. The solution.
> > A similar problem occurred on ARM platforms and was fixed in
> > 08925c2f12 (ARM: 8464/1: Update all mm structures with section
> > adjustments). This patch uses a similar approach to fix the
> > problem on RV32 by synchronizing the memory attributes
> > of the init section for all mm
> >
> > Signed-off-by: CL Wang <cl634@andestech.com>
> > ---
> > arch/riscv/include/asm/set_memory.h | 12 +++++++++
> > arch/riscv/kernel/setup.c | 40 +++++++++++++++++++++++++----
> > arch/riscv/mm/pageattr.c | 30 ++++++++++++++--------
> > 3 files changed, 66 insertions(+), 16 deletions(-)
> >
> > diff --git a/arch/riscv/include/asm/set_memory.h b/arch/riscv/include/asm/set_memory.h
> > index a2c14d4b3993..041551bf568e 100644
> > --- a/arch/riscv/include/asm/set_memory.h
> > +++ b/arch/riscv/include/asm/set_memory.h
> > @@ -16,6 +16,10 @@ 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);
> > +
> > +#if defined(CONFIG_32BIT) && defined(CONFIG_STRICT_KERNEL_RWX)
> > +int set_memory_rw_nx_by_mm(unsigned long addr, int numpages, struct mm_struct *mm);
> > +#endif
> > static __always_inline int set_kernel_memory(char *startp, char *endp,
> > int (*set_memory)(unsigned long start,
> > int num_pages))
> > @@ -32,6 +36,14 @@ 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 int set_memory_rw_nx(unsigned long addr, int numpages) { return 0; }
> > +
> > +#if defined(CONFIG_32BIT) && defined(CONFIG_STRICT_KERNEL_RWX)
> > +static inline int set_memory_rw_nx_by_mm(unsigned long addr,
> > + int numpages, struct mm_struct *mm)
> > +{
> > + return 0;
> > +}
> > +#endif
> > static inline int set_kernel_memory(char *startp, char *endp,
> > int (*set_memory)(unsigned long start,
> > int num_pages))
> > diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c
> > index 5424d7631502..73c221b3c399 100644
> > --- a/arch/riscv/kernel/setup.c
> > +++ b/arch/riscv/kernel/setup.c
> > @@ -319,13 +319,43 @@ static int __init topology_init(void)
> > }
> > subsys_initcall(topology_init);
> >
> > -void free_initmem(void)
> > +#if defined(CONFIG_32BIT) && defined(CONFIG_STRICT_KERNEL_RWX)
> > +static void set_kernel_mm_early(char *startp, char *endp,
> > + int (*set_memory)(unsigned long start,
> > + int num_pages, struct mm_struct *mm))
> > {
> > - if (IS_ENABLED(CONFIG_STRICT_KERNEL_RWX)) {
> > - set_kernel_memory(lm_alias(__init_begin), lm_alias(__init_end), set_memory_rw_nx);
> > - if (IS_ENABLED(CONFIG_64BIT))
> > - set_kernel_memory(__init_begin, __init_end, set_memory_nx);
> > + struct task_struct *t, *s;
> > + unsigned long start = (unsigned long)startp;
> > + unsigned long end = (unsigned long)endp;
> > + int num_pages = PAGE_ALIGN(end - start) >> PAGE_SHIFT;
> > +
> > + set_memory(start, num_pages, current->active_mm);
> > + if (current->active_mm != &init_mm)
> > + set_memory(start, num_pages, &init_mm);
> > +
> > + for_each_process(t) {
> > + if (t->flags & PF_KTHREAD)
> > + continue;
> > + for_each_thread(t, s) {
> > + if (s->mm)
> > + set_memory(start, num_pages, s->mm);
> > + }
> > }
> > +}
> > +#endif
> > +
> > +void free_initmem(void)
> > +{
> > +#ifdef CONFIG_STRICT_KERNEL_RWX
> > +#ifdef CONFIG_32BIT
> > + set_kernel_mm_early(lm_alias(__init_begin), lm_alias(__init_end),
> > + set_memory_rw_nx_by_mm);
> > +#else
> > + set_kernel_memory(lm_alias(__init_begin), lm_alias(__init_end), set_memory_rw_nx);
> > +#endif
> > + if (IS_ENABLED(CONFIG_64BIT))
> > + set_kernel_memory(__init_begin, __init_end, set_memory_nx);
> > +#endif
> >
> > free_initmem_default(POISON_FREE_INITMEM);
> > }
> > diff --git a/arch/riscv/mm/pageattr.c b/arch/riscv/mm/pageattr.c
> > index ea3d61de065b..16ed5cc8f683 100644
> > --- a/arch/riscv/mm/pageattr.c
> > +++ b/arch/riscv/mm/pageattr.c
> > @@ -105,7 +105,7 @@ static const struct mm_walk_ops pageattr_ops = {
> > };
> >
> > static int __set_memory(unsigned long addr, int numpages, pgprot_t set_mask,
> > - pgprot_t clear_mask)
> > + pgprot_t clear_mask, struct mm_struct *mm)
> > {
> > int ret;
> > unsigned long start = addr;
> > @@ -118,42 +118,50 @@ static int __set_memory(unsigned long addr, int numpages, pgprot_t set_mask,
> > if (!numpages)
> > return 0;
> >
> > - mmap_write_lock(&init_mm);
> > - ret = walk_page_range_novma(&init_mm, start, end, &pageattr_ops, NULL,
> > + mmap_write_lock(mm);
> > + ret = walk_page_range_novma(mm, start, end, &pageattr_ops, NULL,
> > &masks);
> > - mmap_write_unlock(&init_mm);
> > + mmap_write_unlock(mm);
> >
> > flush_tlb_kernel_range(start, end);
> >
> > return ret;
> > }
> >
> > +#if defined(CONFIG_32BIT) && defined(CONFIG_STRICT_KERNEL_RWX)
> > +int set_memory_rw_nx_by_mm(unsigned long addr, int numpages, struct mm_struct *mm)
> > +{
> > + return __set_memory(addr, numpages, __pgprot(_PAGE_READ | _PAGE_WRITE),
> > + __pgprot(_PAGE_EXEC), mm);
> > +}
> > +#endif
> > +
> > int set_memory_rw_nx(unsigned long addr, int numpages)
> > {
> > return __set_memory(addr, numpages, __pgprot(_PAGE_READ | _PAGE_WRITE),
> > - __pgprot(_PAGE_EXEC));
> > + __pgprot(_PAGE_EXEC), &init_mm);
> > }
> >
> > int set_memory_ro(unsigned long addr, int numpages)
> > {
> > return __set_memory(addr, numpages, __pgprot(_PAGE_READ),
> > - __pgprot(_PAGE_WRITE));
> > + __pgprot(_PAGE_WRITE), &init_mm);
> > }
> >
> > int set_memory_rw(unsigned long addr, int numpages)
> > {
> > return __set_memory(addr, numpages, __pgprot(_PAGE_READ | _PAGE_WRITE),
> > - __pgprot(0));
> > + __pgprot(0), &init_mm);
> > }
> >
> > int set_memory_x(unsigned long addr, int numpages)
> > {
> > - return __set_memory(addr, numpages, __pgprot(_PAGE_EXEC), __pgprot(0));
> > + return __set_memory(addr, numpages, __pgprot(_PAGE_EXEC), __pgprot(0), &init_mm);
> > }
> >
> > int set_memory_nx(unsigned long addr, int numpages)
> > {
> > - return __set_memory(addr, numpages, __pgprot(0), __pgprot(_PAGE_EXEC));
> > + return __set_memory(addr, numpages, __pgprot(0), __pgprot(_PAGE_EXEC), &init_mm);
> > }
> >
> > int set_direct_map_invalid_noflush(struct page *page)
> > @@ -198,10 +206,10 @@ void __kernel_map_pages(struct page *page, int numpages, int enable)
> >
> > if (enable)
> > __set_memory((unsigned long)page_address(page), numpages,
> > - __pgprot(_PAGE_PRESENT), __pgprot(0));
> > + __pgprot(_PAGE_PRESENT), __pgprot(0), &init_mm);
> > else
> > __set_memory((unsigned long)page_address(page), numpages,
> > - __pgprot(0), __pgprot(_PAGE_PRESENT));
> > + __pgprot(0), __pgprot(_PAGE_PRESENT), &init_mm);
> > }
> > #endif
> >
> > --
> > 2.34.1
> >
>
> Just a short note to tell you that I intend to review this, I just
> need to find some time, hopefully next week :) Thanks for your patch,
> this is very interesting!