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    SubjectRe: [PATCH v2] powerpc: fix boot on BOOK3S_32 with CONFIG_STRICT_KERNEL_RWX
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    Le 22/11/2017 à 12:48, Michael Ellerman a écrit :
    > Christophe LEROY <christophe.leroy@c-s.fr> writes:
    >
    >> Le 22/11/2017 à 00:07, Balbir Singh a écrit :
    >>> On Wed, Nov 22, 2017 at 1:28 AM, Christophe Leroy
    >>> <christophe.leroy@c-s.fr> wrote:
    >>>> On powerpc32, patch_instruction() is called by apply_feature_fixups()
    >>>> which is called from early_init()
    >>>>
    >>>> There is the following note in front of early_init():
    >>>> * Note that the kernel may be running at an address which is different
    >>>> * from the address that it was linked at, so we must use RELOC/PTRRELOC
    >>>> * to access static data (including strings). -- paulus
    >>>>
    >>>> Therefore, slab_is_available() cannot be called yet, and
    >>>> text_poke_area must be addressed with PTRRELOC()
    >>>>
    >>>> Fixes: 37bc3e5fd764f ("powerpc/lib/code-patching: Use alternate map
    >>>> for patch_instruction()")
    >>>> Reported-by: Meelis Roos <mroos@linux.ee>
    >>>> Cc: Balbir Singh <bsingharora@gmail.com>
    >>>> Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
    >>>> ---
    >>>> v2: Added missing asm/setup.h
    >>>>
    >>>> arch/powerpc/lib/code-patching.c | 6 ++----
    >>>> 1 file changed, 2 insertions(+), 4 deletions(-)
    >>>>
    >>>> diff --git a/arch/powerpc/lib/code-patching.c b/arch/powerpc/lib/code-patching.c
    >>>> index c9de03e0c1f1..d469224c4ada 100644
    >>>> --- a/arch/powerpc/lib/code-patching.c
    >>>> +++ b/arch/powerpc/lib/code-patching.c
    >>>> @@ -21,6 +21,7 @@
    >>>> #include <asm/tlbflush.h>
    >>>> #include <asm/page.h>
    >>>> #include <asm/code-patching.h>
    >>>> +#include <asm/setup.h>
    >>>>
    >>>> static int __patch_instruction(unsigned int *addr, unsigned int instr)
    >>>> {
    >>>> @@ -146,11 +147,8 @@ int patch_instruction(unsigned int *addr, unsigned int instr)
    >>>> * During early early boot patch_instruction is called
    >>>> * when text_poke_area is not ready, but we still need
    >>>> * to allow patching. We just do the plain old patching
    >>>> - * We use slab_is_available and per cpu read * via this_cpu_read
    >>>> - * of text_poke_area. Per-CPU areas might not be up early
    >>>> - * this can create problems with just using this_cpu_read()
    >>>> */
    >>>> - if (!slab_is_available() || !this_cpu_read(text_poke_area))
    >>>> + if (!this_cpu_read(*PTRRELOC(&text_poke_area)))
    >>>> return __patch_instruction(addr, instr);
    >>>
    >>> On ppc64, we call apply_feature_fixups() in early_setup() after we've
    >>> relocated ourselves. Sorry for missing the ppc32 case. I would like to
    >>> avoid PTRRELOC when unnecessary.
    >>
    >> What do you suggest then ?
    >>
    >> Some #ifdef PPC32 around that ?
    >
    > No I don't think that improves anything.
    >
    > I think the comment about per-cpu not being up is wrong, you'll just get
    > the static version of text_poke_area, which should be NULL. So we don't
    > need the slab_available() check anyway.
    >
    > So I'll take this as-is.
    >
    > Having said that I absolutely hate PTRRELOC, so if it starts spreading
    > we will have to come up with something less bug prone.

    Would something like that be the solution ?

    diff --git a/arch/powerpc/include/asm/code-patching.h
    b/arch/powerpc/include/asm/code-patching.h
    index abef812de7f8..1c8dd340f5fc 100644
    --- a/arch/powerpc/include/asm/code-patching.h
    +++ b/arch/powerpc/include/asm/code-patching.h
    @@ -30,7 +30,11 @@ unsigned int create_branch(const unsigned int *addr,
    unsigned int create_cond_branch(const unsigned int *addr,
    unsigned long target, int flags);
    int patch_branch(unsigned int *addr, unsigned long target, int flags);
    -int patch_instruction(unsigned int *addr, unsigned int instr);
    +int patch_instruction_early(unsigned int *addr, unsigned int instr,
    bool early);
    +static inline int patch_instruction(unsigned int *addr, unsigned int instr)
    +{
    + return patch_instruction_early(addr, instr, false);
    +}

    int instr_is_relative_branch(unsigned int instr);
    int instr_is_branch_to_addr(const unsigned int *instr, unsigned long
    addr);
    diff --git a/arch/powerpc/lib/code-patching.c
    b/arch/powerpc/lib/code-patching.c
    index d469224c4ada..84ebf9203e40 100644
    --- a/arch/powerpc/lib/code-patching.c
    +++ b/arch/powerpc/lib/code-patching.c
    @@ -135,7 +135,7 @@ static inline int unmap_patch_area(unsigned long addr)
    return 0;
    }

    -int patch_instruction(unsigned int *addr, unsigned int instr)
    +int patch_instruction_early(unsigned int *addr, unsigned int instr,
    bool early)
    {
    int err;
    unsigned int *dest = NULL;
    @@ -148,7 +148,7 @@ int patch_instruction(unsigned int *addr, unsigned
    int instr)
    * when text_poke_area is not ready, but we still need
    * to allow patching. We just do the plain old patching
    */
    - if (!this_cpu_read(*PTRRELOC(&text_poke_area)))
    + if (early || !this_cpu_read(text_poke_area))
    return __patch_instruction(addr, instr);

    local_irq_save(flags);
    @@ -182,13 +182,13 @@ int patch_instruction(unsigned int *addr, unsigned
    int instr)
    }
    #else /* !CONFIG_STRICT_KERNEL_RWX */

    -int patch_instruction(unsigned int *addr, unsigned int instr)
    +int patch_instruction_early(unsigned int *addr, unsigned int instr,
    bool early)
    {
    return __patch_instruction(addr, instr);
    }

    #endif /* CONFIG_STRICT_KERNEL_RWX */
    -NOKPROBE_SYMBOL(patch_instruction);
    +NOKPROBE_SYMBOL(patch_instruction_early);

    int patch_branch(unsigned int *addr, unsigned long target, int flags)
    {
    diff --git a/arch/powerpc/lib/feature-fixups.c
    b/arch/powerpc/lib/feature-fixups.c
    index 41cf5ae273cf..4c98ece9e558 100644
    --- a/arch/powerpc/lib/feature-fixups.c
    +++ b/arch/powerpc/lib/feature-fixups.c
    @@ -45,7 +45,8 @@ static unsigned int *calc_addr(struct fixup_entry
    *fcur, long offset)
    }

    static int patch_alt_instruction(unsigned int *src, unsigned int *dest,
    - unsigned int *alt_start, unsigned int *alt_end)
    + unsigned int *alt_start, unsigned int *alt_end,
    + bool early)
    {
    unsigned int instr;

    @@ -62,12 +63,13 @@ static int patch_alt_instruction(unsigned int *src,
    unsigned int *dest,
    }
    }

    - patch_instruction(dest, instr);
    + patch_instruction_early(dest, instr, early);

    return 0;
    }

    -static int patch_feature_section(unsigned long value, struct
    fixup_entry *fcur)
    +static int __patch_feature_section(unsigned long value, struct
    fixup_entry *fcur,
    + bool early)
    {
    unsigned int *start, *end, *alt_start, *alt_end, *src, *dest;

    @@ -86,17 +88,18 @@ static int patch_feature_section(unsigned long
    value, struct fixup_entry *fcur)
    dest = start;

    for (; src < alt_end; src++, dest++) {
    - if (patch_alt_instruction(src, dest, alt_start, alt_end))
    + if (patch_alt_instruction(src, dest, alt_start, alt_end, early))
    return 1;
    }

    for (; dest < end; dest++)
    - patch_instruction(dest, PPC_INST_NOP);
    + patch_instruction_early(dest, PPC_INST_NOP, early);

    return 0;
    }

    -void do_feature_fixups(unsigned long value, void *fixup_start, void
    *fixup_end)
    +static void __do_feature_fixups(unsigned long value, void *fixup_start,
    + void *fixup_end, bool early)
    {
    struct fixup_entry *fcur, *fend;

    @@ -104,7 +107,7 @@ void do_feature_fixups(unsigned long value, void
    *fixup_start, void *fixup_end)
    fend = fixup_end;

    for (; fcur < fend; fcur++) {
    - if (patch_feature_section(value, fcur)) {
    + if (__patch_feature_section(value, fcur, early)) {
    WARN_ON(1);
    printk("Unable to patch feature section at %p - %p" \
    " with %p - %p\n",
    @@ -116,7 +119,13 @@ void do_feature_fixups(unsigned long value, void
    *fixup_start, void *fixup_end)
    }
    }

    -void do_lwsync_fixups(unsigned long value, void *fixup_start, void
    *fixup_end)
    +void do_feature_fixups(unsigned long value, void *fixup_start, void
    *fixup_end)
    +{
    + __do_feature_fixups(value, fixup_start, fixup_end, false);
    +}
    +
    +static void __do_lwsync_fixups(unsigned long value, void *fixup_start,
    + void *fixup_end, bool early)
    {
    long *start, *end;
    unsigned int *dest;
    @@ -129,10 +138,15 @@ void do_lwsync_fixups(unsigned long value, void
    *fixup_start, void *fixup_end)

    for (; start < end; start++) {
    dest = (void *)start + *start;
    - patch_instruction(dest, PPC_INST_LWSYNC);
    + patch_instruction_early(dest, PPC_INST_LWSYNC, early);
    }
    }

    +void do_lwsync_fixups(unsigned long value, void *fixup_start, void
    *fixup_end)
    +{
    + __do_lwsync_fixups(value, fixup_start, fixup_end, false);
    +}
    +
    static void do_final_fixups(void)
    {
    #if defined(CONFIG_PPC64) && defined(CONFIG_RELOCATABLE)
    @@ -147,7 +161,7 @@ static void do_final_fixups(void)
    length = (__end_interrupts - _stext) / sizeof(int);

    while (length--) {
    - patch_instruction(dest, *src);
    + patch_instruction_early(dest, *src, true);
    src++;
    dest++;
    }
    @@ -171,22 +185,23 @@ void __init apply_feature_fixups(void)
    * Apply the CPU-specific and firmware specific fixups to kernel text
    * (nop out sections not relevant to this CPU or this firmware).
    */
    - do_feature_fixups(spec->cpu_features,
    + __do_feature_fixups(spec->cpu_features,
    PTRRELOC(&__start___ftr_fixup),
    - PTRRELOC(&__stop___ftr_fixup));
    + PTRRELOC(&__stop___ftr_fixup), true);

    - do_feature_fixups(spec->mmu_features,
    + __do_feature_fixups(spec->mmu_features,
    PTRRELOC(&__start___mmu_ftr_fixup),
    - PTRRELOC(&__stop___mmu_ftr_fixup));
    + PTRRELOC(&__stop___mmu_ftr_fixup), true);

    - do_lwsync_fixups(spec->cpu_features,
    + __do_lwsync_fixups(spec->cpu_features,
    PTRRELOC(&__start___lwsync_fixup),
    - PTRRELOC(&__stop___lwsync_fixup));
    + PTRRELOC(&__stop___lwsync_fixup), true);

    #ifdef CONFIG_PPC64
    saved_firmware_features = powerpc_firmware_features;
    do_feature_fixups(powerpc_firmware_features,
    - &__start___fw_ftr_fixup, &__stop___fw_ftr_fixup);
    + &__start___fw_ftr_fixup, &__stop___fw_ftr_fixup,
    + true);
    #endif
    do_final_fixups();
    }
    @@ -226,6 +241,11 @@ late_initcall(check_features);
    /* This must be after the text it fixes up, vmlinux.lds.S enforces
    that atm */
    static struct fixup_entry fixup;

    +static int patch_feature_section(unsigned long value, struct
    fixup_entry *fcur)
    +{
    + return __patch_feature_section(value, fcur, false);
    +}
    +
    static long calc_offset(struct fixup_entry *entry, unsigned int *p)
    {
    return (unsigned long)p - (unsigned long)entry;

    Christophe

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