Re: [PATCH v4 03/15] arm64: Detect if in a realm and set RIPAS RAM

Gavin Shan
2024-07-31T07:03:21Z

Hi Suzuki,

On 7/30/24 11:51 PM, Suzuki K Poulose wrote:
> On 30/07/2024 00:37, Gavin Shan wrote:
>> On 7/1/24 7:54 PM, Steven Price wrote:
>>> From: Suzuki K Poulose <suzuki.poulose@arm.com>
>>>
>>> Detect that the VM is a realm guest by the presence of the RSI
>>> interface.
>>>
>>> If in a realm then all memory needs to be marked as RIPAS RAM initially,
>>> the loader may or may not have done this for us. To be sure iterate over
>>> all RAM and mark it as such. Any failure is fatal as that implies the
>>> RAM regions passed to Linux are incorrect - which would mean failing
>>> later when attempting to access non-existent RAM.
>>>
>>> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
>>> Co-developed-by: Steven Price <steven.price@arm.com>
>>> Signed-off-by: Steven Price <steven.price@arm.com>
>>> ---
>>> Changes since v3:
>>>   * Provide safe/unsafe versions for converting memory to protected,
>>>     using the safer version only for the early boot.
>>>   * Use the new psci_early_test_conduit() function to avoid calling an
>>>     SMC if EL3 is not present (or not configured to handle an SMC).
>>> Changes since v2:
>>>   * Use DECLARE_STATIC_KEY_FALSE rather than "extern struct
>>>     static_key_false".
>>>   * Rename set_memory_range() to rsi_set_memory_range().
>>>   * Downgrade some BUG()s to WARN()s and handle the condition by
>>>     propagating up the stack. Comment the remaining case that ends in a
>>>     BUG() to explain why.
>>>   * Rely on the return from rsi_request_version() rather than checking
>>>     the version the RMM claims to support.
>>>   * Rename the generic sounding arm64_setup_memory() to
>>>     arm64_rsi_setup_memory() and move the call site to setup_arch().
>>> ---
>>>   arch/arm64/include/asm/rsi.h      | 64 +++++++++++++++++++++++++
>>>   arch/arm64/include/asm/rsi_cmds.h | 22 +++++++++
>>>   arch/arm64/kernel/Makefile        |  3 +-
>>>   arch/arm64/kernel/rsi.c           | 77 +++++++++++++++++++++++++++++++
>>>   arch/arm64/kernel/setup.c         |  8 ++++
>>>   5 files changed, 173 insertions(+), 1 deletion(-)
>>>   create mode 100644 arch/arm64/include/asm/rsi.h
>>>   create mode 100644 arch/arm64/kernel/rsi.c
>>>
>>> diff --git a/arch/arm64/include/asm/rsi.h b/arch/arm64/include/asm/rsi.h
>>> new file mode 100644
>>> index 000000000000..29fdc194d27b
>>> --- /dev/null
>>> +++ b/arch/arm64/include/asm/rsi.h
>>> @@ -0,0 +1,64 @@
>>> +/* SPDX-License-Identifier: GPL-2.0-only */
>>> +/*
>>> + * Copyright (C) 2024 ARM Ltd.
>>> + */
>>> +
>>> +#ifndef __ASM_RSI_H_
>>> +#define __ASM_RSI_H_
>>> +
>>> +#include <linux/jump_label.h>
>>> +#include <asm/rsi_cmds.h>
>>> +
>>> +DECLARE_STATIC_KEY_FALSE(rsi_present);
>>> +
>>> +void __init arm64_rsi_init(void);
>>> +void __init arm64_rsi_setup_memory(void);
>>> +static inline bool is_realm_world(void)
>>> +{
>>> +    return static_branch_unlikely(&rsi_present);
>>> +}
>>> +
>>> +static inline int rsi_set_memory_range(phys_addr_t start, phys_addr_t end,
>>> +                       enum ripas state, unsigned long flags)
>>> +{
>>> +    unsigned long ret;
>>> +    phys_addr_t top;
>>> +
>>> +    while (start != end) {
>>> +        ret = rsi_set_addr_range_state(start, end, state, flags, &top);
>>> +        if (WARN_ON(ret || top < start || top > end))
>>> +            return -EINVAL;
>>> +        start = top;
>>> +    }
>>> +
>>> +    return 0;
>>> +}
>>> +
>>
>> @flags has been defined as int instead of unsigned long, which is inconsistent
>> to TF-RMM's definitions since it has type of 'unsigned long'.
>
> Sorry, do you mean that TF-RMM treats the "flags" as an "int" instead of
> unsigned long and we should be consistent with TF-RMM ? If so, I don't
> think that is correct. We should be compliant to the RMM spec, which
> describes "RsiRipasChangeFlags" as a 64bit value and thus must be
> 'unsigned long' as we used here.
>

No worries, I guess I didn't make myself clear enough. Sorry about that.
Let me explain it with more details. @flag is passed down as the following
call trace shows.

rsi_set_memory_range_protected_safe
rsi_set_memory_range // RSI_NO_CHANGE_DESTROYED
rsi_set_addr_range_state
arm_smccc_smc(SMC_RSI_IPA_STATE_SET, ...)

The kernel defines RSI_CHANGE_DESTROYED as a "int" value, but same flag has
been defined as 'unsigned int' value in tf-rmm. However, kernel uses 'unsigned
long' flags to hold it.

// kernel's prototype - 'unsigned long flags'
static inline int rsi_set_memory_range(phys_addr_t start, phys_addr_t end,
enum ripas state, unsigned long flags)

// kernel's definition - 'int'
#define RSI_CHANGE_DESTROYED 0

// tf-rmm's definition - 'unsigned int'
#define U(_x) (unsigned int)(_x)
#define RSI_CHANGE_DESTROYED U(0)

>>
>>> +/*
>>> + * Convert the specified range to RAM. Do not use this if you rely on the
>>> + * contents of a page that may already be in RAM state.
>>> + */
>>> +static inline int rsi_set_memory_range_protected(phys_addr_t start,
>>> +                         phys_addr_t end)
>>> +{
>>> +    return rsi_set_memory_range(start, end, RSI_RIPAS_RAM,
>>> +                    RSI_CHANGE_DESTROYED);
>>> +}
>>> +
>>> +/*
>>> + * Convert the specified range to RAM. Do not convert any pages that may have
>>> + * been DESTROYED, without our permission.
>>> + */
>>> +static inline int rsi_set_memory_range_protected_safe(phys_addr_t start,
>>> +                              phys_addr_t end)
>>> +{
>>> +    return rsi_set_memory_range(start, end, RSI_RIPAS_RAM,
>>> +                    RSI_NO_CHANGE_DESTROYED);
>>> +}
>>> +
>>> +static inline int rsi_set_memory_range_shared(phys_addr_t start,
>>> +                          phys_addr_t end)
>>> +{
>>> +    return rsi_set_memory_range(start, end, RSI_RIPAS_EMPTY, 0);
>>> +}
>>> +#endif
>>
>> s/0/RSI_NO_CHANGE_DESTROYED
>
> This is not required as we do not care if the GRANULE was destroyed or
> not, since it is going to be "UNUSED" anyway in a protected way (RIPAS_EMPTY). And we do not rely on the contents of the memory being
> preserved, when the page is made shared (In fact we cannot do that
> with Arm CCA).
>
> Thus we do not get any security benefits with the flag. The flag is ONLY
> useful, when the Realm does a "blanket" IPA_STATE_SET(RIPAS_RAM) for
> all of its memory area described as RAM. In this case, we want to make
> sure that the Host hasn't destroyed any DATA that was loaded (and
> measured) in the "NEW" state.
>
> e.g, Host loads Kernel at Addr X in RAM (which is transitioned to RIPAS_RAM, measured in RIM by RMM) and ACTIVATEs the Realm. Host could then destroy some pages of the loaded image before the Realm boots (thus
> transitioning into DESTROYED). But for the Realm, at early boot, it is
> much easier to "mark" the entire RAM region as RIPAS_RAM,
>
>
> for_each_memory_region(region) {
>     set_ipa_state_range(region->start, region->end, RIPAS_RAM, RSI_NO_CHANGE_DESTROYED);
> }
>
> rather than performing:
>
> for_each_granule(g in DRAM) :
>
> switch (rsi_get_ipa_state(g)) {
> case RIPAS_EMPTY: rsi_set_ipa_state(g, RIPAS_RAM); break;
> case RIPAS_RAM: break; /* Nothing to do */
> case DESTROYED: BUG();
> }
>
>

The point was 0 and RSI_NO_CHANGE_DESTROYED are interchangeable. Since RSI_NO_CHANGE_DESTROYED
has been defined as 0, why we don't used RSI_NO_CHANGE_DESTROYED?

>
>> s/#endif/#endif /* __ASM_RSI_H_ */
>>
>>> diff --git a/arch/arm64/include/asm/rsi_cmds.h b/arch/arm64/include/asm/rsi_cmds.h
>>> index 89e907f3af0c..acb557dd4b88 100644
>>> --- a/arch/arm64/include/asm/rsi_cmds.h
>>> +++ b/arch/arm64/include/asm/rsi_cmds.h
>>> @@ -10,6 +10,11 @@
>>>   #include <asm/rsi_smc.h>
>>> +enum ripas {
>>> +    RSI_RIPAS_EMPTY,
>>> +    RSI_RIPAS_RAM,
>>> +};
>>> +
>>>   static inline unsigned long rsi_request_version(unsigned long req,
>>>                           unsigned long *out_lower,
>>>                           unsigned long *out_higher)
>>> @@ -35,4 +40,21 @@ static inline unsigned long rsi_get_realm_config(struct realm_config *cfg)
>>>       return res.a0;
>>>   }
>>> +static inline unsigned long rsi_set_addr_range_state(phys_addr_t start,
>>> +                             phys_addr_t end,
>>> +                             enum ripas state,
>>> +                             unsigned long flags,
>>> +                             phys_addr_t *top)
>>> +{
>>> +    struct arm_smccc_res res;
>>> +
>>> +    arm_smccc_smc(SMC_RSI_IPA_STATE_SET, start, end, state,
>>> +              flags, 0, 0, 0, &res);
>>> +
>>> +    if (top)
>>> +        *top = res.a1;
>>> +
>>> +    return res.a0;
>>> +}
>>> +
>>>   #endif
>>> diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
>>> index 763824963ed1..a483b916ed11 100644
>>> --- a/arch/arm64/kernel/Makefile
>>> +++ b/arch/arm64/kernel/Makefile
>>> @@ -33,7 +33,8 @@ obj-y            := debug-monitors.o entry.o irq.o fpsimd.o        \
>>>                  return_address.o cpuinfo.o cpu_errata.o        \
>>>                  cpufeature.o alternative.o cacheinfo.o        \
>>>                  smp.o smp_spin_table.o topology.o smccc-call.o    \
>>> -               syscall.o proton-pack.o idle.o patching.o pi/
>>> +               syscall.o proton-pack.o idle.o patching.o pi/    \
>>> +               rsi.o
>>>   obj-$(CONFIG_COMPAT)            += sys32.o signal32.o            \
>>>                          sys_compat.o
>>> diff --git a/arch/arm64/kernel/rsi.c b/arch/arm64/kernel/rsi.c
>>> new file mode 100644
>>> index 000000000000..f01bff9dab04
>>> --- /dev/null
>>> +++ b/arch/arm64/kernel/rsi.c
>>> @@ -0,0 +1,77 @@
>>> +// SPDX-License-Identifier: GPL-2.0-only
>>> +/*
>>> + * Copyright (C) 2023 ARM Ltd.
>>> + */
>>> +
>>> +#include <linux/jump_label.h>
>>> +#include <linux/memblock.h>
>>> +#include <linux/psci.h>
>>> +#include <asm/rsi.h>
>>> +
>>> +DEFINE_STATIC_KEY_FALSE_RO(rsi_present);
>>> +EXPORT_SYMBOL(rsi_present);
>>> +
>>> +static bool rsi_version_matches(void)
>>> +{
>>> +    unsigned long ver_lower, ver_higher;
>>> +    unsigned long ret = rsi_request_version(RSI_ABI_VERSION,
>>> +                        &ver_lower,
>>> +                        &ver_higher);
>>> +
>>> +    if (ret == SMCCC_RET_NOT_SUPPORTED)
>>> +        return false;
>>> +
>>> +    if (ret != RSI_SUCCESS) {
>>> +        pr_err("RME: RMM doesn't support RSI version %u.%u. Supported range: %lu.%lu-%lu.%lu\n",
>>> +               RSI_ABI_VERSION_MAJOR, RSI_ABI_VERSION_MINOR,
>>> +               RSI_ABI_VERSION_GET_MAJOR(ver_lower),
>>> +               RSI_ABI_VERSION_GET_MINOR(ver_lower),
>>> +               RSI_ABI_VERSION_GET_MAJOR(ver_higher),
>>> +               RSI_ABI_VERSION_GET_MINOR(ver_higher));
>>> +        return false;
>>> +    }
>>> +
>>> +    pr_info("RME: Using RSI version %lu.%lu\n",
>>> +        RSI_ABI_VERSION_GET_MAJOR(ver_lower),
>>> +        RSI_ABI_VERSION_GET_MINOR(ver_lower));
>>> +
>>> +    return true;
>>> +}
>>> +
>>> +void __init arm64_rsi_setup_memory(void)
>>> +{
>>> +    u64 i;
>>> +    phys_addr_t start, end;
>>> +
>>> +    if (!is_realm_world())
>>> +        return;
>>> +
>>> +    /*
>>> +     * Iterate over the available memory ranges and convert the state to
>> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>>                                               blocks and convert them to
>
> TBH, I don't see any significant difference between the two. Am I
> missing something ?
>

for_each_mem_range() is a helper provided by memory block management module.
So 'memory block' sounds like more accurate than broadly used term "memory
range" here.

>>
>>> +     * protected memory. We should take extra care to ensure that we DO NOT
>>> +     * permit any "DESTROYED" pages to be converted to "RAM".
>>> +     *
>>> +     * BUG_ON is used because if the attempt to switch the memory to
>>> +     * protected has failed here, then future accesses to the memory are
>>> +     * simply going to be reflected as a fault which we can't handle.
>>> +     * Bailing out early prevents the guest limping on and dieing later.
>>> +     */
>>> +    for_each_mem_range(i, &start, &end) {
>>> +        BUG_ON(rsi_set_memory_range_protected_safe(start, end));
>>> +    }
>>> +}
>>> +
>>
>> If I'm understanding the code completely, this changes the memory state from
>> RIPAS_EMPTY to RIPAS_RAM so that the following page faults can be routed to
>> host properly. Otherwise, a SEA is injected to the realm according to
>> tf-rmm/runtime/core/exit.c::handle_data_abort(). The comments can be more
>> explicit to replace "fault" with "SEA (Synchronous External Abort)".
>
> Agreed.  SEA is more accurate than fault.
>

Ok.

>>
>> Besides, this forces a guest exit with reason RMI_EXIT_RIPAS_CHANGE which is
>> handled by the host, where RMI_RTT_SET_RIPAS is triggered to convert the memory
>> state from RIPAS_EMPTY to RIPAS_RAM. The question is why the conversion can't
>> be done by VMM (QEMU)?
>
> A VMM could potentially do this via INIT_RIPAS at Realm creation for
> the entire RAM. But, as far as the Realm is concerned it is always safer to do this step and is relatively a lightweight operation at boot. Physical pages need not be allocated/mapped in stage2 with the IPA State change.
>

Ok. Thanks for the explanation.

>
> Suzuki
>>
>>> +void __init arm64_rsi_init(void)
>>> +{
>>> +    /*
>>> +     * If PSCI isn't using SMC, RMM isn't present. Don't try to execute an
>>> +     * SMC as it could be UNDEFINED.
>>> +     */
>>> +    if (!psci_early_test_conduit(SMCCC_CONDUIT_SMC))
>>> +        return;
>>> +    if (!rsi_version_matches())
>>> +        return;
>>> +
>>> +    static_branch_enable(&rsi_present);
>>> +}
>>> +
>>> diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c
>>> index a096e2451044..143f87615af0 100644
>>> --- a/arch/arm64/kernel/setup.c
>>> +++ b/arch/arm64/kernel/setup.c
>>> @@ -43,6 +43,7 @@
>>>   #include <asm/cpu_ops.h>
>>>   #include <asm/kasan.h>
>>>   #include <asm/numa.h>
>>> +#include <asm/rsi.h>
>>>   #include <asm/scs.h>
>>>   #include <asm/sections.h>
>>>   #include <asm/setup.h>
>>> @@ -293,6 +294,11 @@ void __init __no_sanitize_address setup_arch(char **cmdline_p)
>>>        * cpufeature code and early parameters.
>>>        */
>>>       jump_label_init();
>>> +    /*
>>> +     * Init RSI before early param so that "earlycon" console uses the
>>> +     * shared alias when in a realm
>>> +     */
>>> +    arm64_rsi_init();
>>>       parse_early_param();
>>>       dynamic_scs_init();
>>> @@ -328,6 +334,8 @@ void __init __no_sanitize_address setup_arch(char **cmdline_p)
>>>       arm64_memblock_init();
>>> +    arm64_rsi_setup_memory();
>>> +
>>>       paging_init();
>>>       acpi_table_upgrade();
>>

Thanks,
Gavin