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    Subject[PATCH v4 1/6] powerpc/book3s64/kuap: Improve error reporting with KUAP
    Date
    From: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>

    This partially reverts commit eb232b162446 ("powerpc/book3s64/kuap: Improve
    error reporting with KUAP") and update the fault handler to print

    [ 55.022514] Kernel attempted to access user page (7e6725b70000) - exploit attempt? (uid: 0)
    [ 55.022528] BUG: Unable to handle kernel data access on read at 0x7e6725b70000
    [ 55.022533] Faulting instruction address: 0xc000000000e8b9bc
    [ 55.022540] Oops: Kernel access of bad area, sig: 11 [#1]
    ....

    when the kernel access userspace address without unlocking AMR.

    bad_kuap_fault() is added as part of commit 5e5be3aed230 ("powerpc/mm: Detect
    bad KUAP faults") to catch userspace access incorrectly blocked by AMR. Hence
    retain the full stack dump there even with hash translation. Also, add a comment
    explaining the difference between hash and radix.

    Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
    Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
    ---
    arch/powerpc/include/asm/book3s/32/kup.h | 4 +--
    arch/powerpc/include/asm/book3s/64/kup.h | 34 ++++++++++----------
    arch/powerpc/include/asm/kup.h | 4 +--
    arch/powerpc/include/asm/nohash/32/kup-8xx.h | 4 +--
    arch/powerpc/mm/fault.c | 4 +--
    5 files changed, 25 insertions(+), 25 deletions(-)

    diff --git a/arch/powerpc/include/asm/book3s/32/kup.h b/arch/powerpc/include/asm/book3s/32/kup.h
    index b18cd931e325..32fd4452e960 100644
    --- a/arch/powerpc/include/asm/book3s/32/kup.h
    +++ b/arch/powerpc/include/asm/book3s/32/kup.h
    @@ -177,8 +177,8 @@ static inline void restore_user_access(unsigned long flags)
    allow_user_access(to, to, end - addr, KUAP_READ_WRITE);
    }

    -static inline bool bad_kuap_fault(struct pt_regs *regs, unsigned long address,
    - bool is_write, unsigned long error_code)
    +static inline bool
    +bad_kuap_fault(struct pt_regs *regs, unsigned long address, bool is_write)
    {
    unsigned long begin = regs->kuap & 0xf0000000;
    unsigned long end = regs->kuap << 28;
    diff --git a/arch/powerpc/include/asm/book3s/64/kup.h b/arch/powerpc/include/asm/book3s/64/kup.h
    index f2e6dd78d5e2..7075c92c320c 100644
    --- a/arch/powerpc/include/asm/book3s/64/kup.h
    +++ b/arch/powerpc/include/asm/book3s/64/kup.h
    @@ -353,29 +353,29 @@ static inline void set_kuap(unsigned long value)
    isync();
    }

    -#define RADIX_KUAP_BLOCK_READ UL(0x4000000000000000)
    -#define RADIX_KUAP_BLOCK_WRITE UL(0x8000000000000000)
    -
    static inline bool bad_kuap_fault(struct pt_regs *regs, unsigned long address,
    - bool is_write, unsigned long error_code)
    + bool is_write)
    {
    if (!mmu_has_feature(MMU_FTR_BOOK3S_KUAP))
    return false;
    -
    - if (radix_enabled()) {
    - /*
    - * Will be a storage protection fault.
    - * Only check the details of AMR[0]
    - */
    - return WARN((regs->kuap & (is_write ? RADIX_KUAP_BLOCK_WRITE : RADIX_KUAP_BLOCK_READ)),
    - "Bug: %s fault blocked by AMR!", is_write ? "Write" : "Read");
    - }
    /*
    - * We don't want to WARN here because userspace can setup
    - * keys such that a kernel access to user address can cause
    - * fault
    + * For radix this will be a storage protection fault (DSISR_PROTFAULT).
    + * For hash this will be a key fault (DSISR_KEYFAULT)
    */
    - return !!(error_code & DSISR_KEYFAULT);
    + /*
    + * We do have exception table entry, but accessing the
    + * userspace results in fault. This could be because we
    + * didn't unlock the AMR or access is denied by userspace
    + * using a key value that blocks access. We are only interested
    + * in catching the use case of accessing without unlocking
    + * the AMR. Hence check for BLOCK_WRITE/READ against AMR.
    + */
    + if (is_write) {
    + return WARN(((regs->amr & AMR_KUAP_BLOCK_WRITE) == AMR_KUAP_BLOCK_WRITE),
    + "Bug: Write fault blocked by AMR!");
    + }
    + return WARN(((regs->amr & AMR_KUAP_BLOCK_READ) == AMR_KUAP_BLOCK_READ),
    + "Bug: Read fault blocked by AMR!");
    }

    static __always_inline void allow_user_access(void __user *to, const void __user *from,
    diff --git a/arch/powerpc/include/asm/kup.h b/arch/powerpc/include/asm/kup.h
    index f8ec679bd2de..5a9820c54da9 100644
    --- a/arch/powerpc/include/asm/kup.h
    +++ b/arch/powerpc/include/asm/kup.h
    @@ -62,8 +62,8 @@ void setup_kuap(bool disabled);
    #else
    static inline void setup_kuap(bool disabled) { }

    -static inline bool bad_kuap_fault(struct pt_regs *regs, unsigned long address,
    - bool is_write, unsigned long error_code)
    +static inline bool
    +bad_kuap_fault(struct pt_regs *regs, unsigned long address, bool is_write)
    {
    return false;
    }
    diff --git a/arch/powerpc/include/asm/nohash/32/kup-8xx.h b/arch/powerpc/include/asm/nohash/32/kup-8xx.h
    index 7bdd9e5b63ed..567cdc557402 100644
    --- a/arch/powerpc/include/asm/nohash/32/kup-8xx.h
    +++ b/arch/powerpc/include/asm/nohash/32/kup-8xx.h
    @@ -60,8 +60,8 @@ static inline void restore_user_access(unsigned long flags)
    mtspr(SPRN_MD_AP, flags);
    }

    -static inline bool bad_kuap_fault(struct pt_regs *regs, unsigned long address,
    - bool is_write, unsigned long error_code)
    +static inline bool
    +bad_kuap_fault(struct pt_regs *regs, unsigned long address, bool is_write)
    {
    return WARN(!((regs->kuap ^ MD_APG_KUAP) & 0xff000000),
    "Bug: fault blocked by AP register !");
    diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
    index c91621df0c61..b12595102525 100644
    --- a/arch/powerpc/mm/fault.c
    +++ b/arch/powerpc/mm/fault.c
    @@ -210,7 +210,7 @@ static bool bad_kernel_fault(struct pt_regs *regs, unsigned long error_code,
    return true;
    }

    - if (!is_exec && address < TASK_SIZE && (error_code & DSISR_PROTFAULT) &&
    + if (!is_exec && address < TASK_SIZE && (error_code & (DSISR_PROTFAULT | DSISR_KEYFAULT)) &&
    !search_exception_tables(regs->nip)) {
    pr_crit_ratelimited("Kernel attempted to access user page (%lx) - exploit attempt? (uid: %d)\n",
    address,
    @@ -227,7 +227,7 @@ static bool bad_kernel_fault(struct pt_regs *regs, unsigned long error_code,

    // Read/write fault in a valid region (the exception table search passed
    // above), but blocked by KUAP is bad, it can never succeed.
    - if (bad_kuap_fault(regs, address, is_write, error_code))
    + if (bad_kuap_fault(regs, address, is_write))
    return true;

    // What's left? Kernel fault on user in well defined regions (extable
    --
    2.25.0
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