Re: [Qemu-devel] [Qemu-ppc] [PATCH v2 2/3] hmp: fix "dump-quest-memory" segfault (arm)

[Greg Kurz]

On Mon, 11 Sep 2017 16:20:55 +0200
Laurent Vivier <address@hidden> wrote:

> Commit fd5d23babf (hmp: fix "dump-quest-memory" segfault)
> fixes the problem for i386, do the same for arm.
> 
> Running QEMU with
>     qemu-system-aarch64 -M none -nographic -m 256
> and executing
>     dump-guest-memory /dev/null 0 8192
> results in segfault
> 
> Fix by checking if we have CPU.
> 
> Signed-off-by: Laurent Vivier <address@hidden>
> ---
>  target/arm/arch_dump.c | 52 
> +++++++++++++++++++++++++++++++++-----------------
>  1 file changed, 34 insertions(+), 18 deletions(-)
> 
> diff --git a/target/arm/arch_dump.c b/target/arm/arch_dump.c
> index 1a9861f69b..1f58cff256 100644
> --- a/target/arm/arch_dump.c
> +++ b/target/arm/arch_dump.c
> @@ -273,8 +273,6 @@ int arm_cpu_write_elf32_note(WriteCoreDumpFunction f, 
> CPUState *cs,
>  int cpu_get_dump_info(ArchDumpInfo *info,
>                        const GuestPhysBlockList *guest_phys_blocks)
>  {
> -    ARMCPU *cpu = ARM_CPU(first_cpu);
> -    CPUARMState *env = &cpu->env;
>      GuestPhysBlock *block;
>      hwaddr lowest_addr = ULLONG_MAX;
>  
> @@ -290,13 +288,32 @@ int cpu_get_dump_info(ArchDumpInfo *info,
>          }
>      }
>  
> -    if (arm_feature(env, ARM_FEATURE_AARCH64)) {
> -        info->d_machine = EM_AARCH64;
> -        info->d_class = ELFCLASS64;
> -        info->page_size = (1 << 16); /* aarch64 max pagesize */
> -        if (lowest_addr != ULLONG_MAX) {
> -            info->phys_base = lowest_addr;
> +    if (first_cpu) {
> +        ARMCPU *cpu = ARM_CPU(first_cpu);
> +        CPUARMState *env = &cpu->env;
> +        if (arm_feature(env, ARM_FEATURE_AARCH64)) {
> +            info->d_machine = EM_AARCH64;
> +            info->d_class = ELFCLASS64;
> +            info->page_size = (1 << 16); /* aarch64 max pagesize */
> +            if (lowest_addr != ULLONG_MAX) {
> +                info->phys_base = lowest_addr;
> +            }
> +        } else {
> +            info->d_machine = EM_ARM;
> +            info->d_class = ELFCLASS32;
> +            info->page_size = (1 << 12);
> +            if (lowest_addr < UINT_MAX) {
> +                info->phys_base = lowest_addr;
> +            }
>          }
> +
> +        /* We assume the relevant endianness is that of EL1; this is right
> +         * for kernels, but might give the wrong answer if you're trying to
> +         * dump a hypervisor that happens to be running an opposite-endian
> +         * kernel.
> +         */
> +        info->d_endian = (env->cp15.sctlr_el[1] & SCTLR_EE) != 0
> +                         ? ELFDATA2MSB : ELFDATA2LSB;
>      } else {
>          info->d_machine = EM_ARM;
>          info->d_class = ELFCLASS32;
> @@ -304,25 +321,24 @@ int cpu_get_dump_info(ArchDumpInfo *info,
>          if (lowest_addr < UINT_MAX) {
>              info->phys_base = lowest_addr;
>          }
> +        info->d_endian = ELFDATA2LSB;
>      }
>  
> -    /* We assume the relevant endianness is that of EL1; this is right
> -     * for kernels, but might give the wrong answer if you're trying to
> -     * dump a hypervisor that happens to be running an opposite-endian
> -     * kernel.
> -     */
> -    info->d_endian = (env->cp15.sctlr_el[1] & SCTLR_EE) != 0
> -                     ? ELFDATA2MSB : ELFDATA2LSB;
> -
>      return 0;
>  }
>  
>  ssize_t cpu_get_note_size(int class, int machine, int nr_cpus)
>  {
> -    ARMCPU *cpu = ARM_CPU(first_cpu);
> -    CPUARMState *env = &cpu->env;
> +    ARMCPU *cpu;
> +    CPUARMState *env;
>      size_t note_size;
>  
> +    if (first_cpu == NULL) {
> +        return 0;
> +    }
> +

Looking at the function's code, it seems that env is only needed if
class != ELFCLASS64... I guess that all the code dealing with first_cpu
should go to the else block.

> +    cpu = ARM_CPU(first_cpu);
> +    env = &cpu->env;
>      if (class == ELFCLASS64) {
>          note_size = AARCH64_PRSTATUS_NOTE_SIZE;
>          note_size += AARCH64_PRFPREG_NOTE_SIZE;

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