Subject: Re: [PATCH 2/2] powerpc/perf: Fix the kernel address leak to userspace via SDAR

From: "Naveen N. Rao" <[email-masked]>
Date: Mon, 05 Mar 2018 13:51:21 +0530

Madhavan Srinivasan wrote:
> Sampled Data Address Register (SDAR) is a 64-bit
> register that contains the effective address of
> the storage operand of an instruction that was
> being executed, possibly out-of-order, at or around
> the time that the Performance Monitor alert occurred.
> 
> In certain scenario SDAR happen to contain the kernel
> address even for userspace only sampling. Add checks
> to prevent it.
> 
> Signed-off-by: Madhavan Srinivasan <[email-masked]>
> ---
>  arch/powerpc/perf/core-book3s.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c
> index 337db5831749..c4525323d691 100644
> --- a/arch/powerpc/perf/core-book3s.c
> +++ b/arch/powerpc/perf/core-book3s.c
> @@ -95,7 +95,7 @@ static inline unsigned long perf_ip_adjust(struct pt_regs *regs)
>  {
>  	return 0;
>  }
> -static inline void perf_get_data_addr(struct pt_regs *regs, u64 *addrp) { }
> +static inline void perf_get_data_addr(struct pt_regs *regs, u64 *addrp, struct perf_event *event) { }
>  static inline u32 perf_get_misc_flags(struct pt_regs *regs)
>  {
>  	return 0;
> @@ -174,7 +174,7 @@ static inline unsigned long perf_ip_adjust(struct pt_regs *regs)
>   * pointed to by SIAR; this is indicated by the [POWER6_]MMCRA_SDSYNC, the
>   * [POWER7P_]MMCRA_SDAR_VALID bit in MMCRA, or the SDAR_VALID bit in SIER.
>   */
> -static inline void perf_get_data_addr(struct pt_regs *regs, u64 *addrp)
> +static inline void perf_get_data_addr(struct pt_regs *regs, u64 *addrp, struct perf_event *event)
>  {
>  	unsigned long mmcra = regs->dsisr;
>  	bool sdar_valid;
> @@ -198,6 +198,11 @@ static inline void perf_get_data_addr(struct pt_regs *regs, u64 *addrp)
> 
>  	if (!(mmcra & MMCRA_SAMPLE_ENABLE) || sdar_valid)
>  		*addrp = mfspr(SPRN_SDAR);
> +
> +	if (perf_paranoid_kernel() && !capable(CAP_SYS_ADMIN) &&
> +		(event->attr.exclude_kernel || event->attr.exclude_hv) &&

I may be missing something, but if !capable(CAP_SYS_ADMIN), should we 
still check the exclude_kernel/exclude_hv fields in the event attribute?  
Aren't those user controlled?

- Naveen

> +		is_kernel_addr(mfspr(SPRN_SDAR)))
> +		*addrp = 0;
>  }
> 
>  static bool regs_sihv(struct pt_regs *regs)
> @@ -2054,7 +2059,7 @@ static void record_and_restart(struct perf_event *event, unsigned long val,
> 
>  		if (event->attr.sample_type &
>  		    (PERF_SAMPLE_ADDR | PERF_SAMPLE_PHYS_ADDR))
> -			perf_get_data_addr(regs, &data.addr);
> +			perf_get_data_addr(regs, &data.addr, event);
> 
>  		if (event->attr.sample_type & PERF_SAMPLE_BRANCH_STACK) {
>  			struct cpu_hw_events *cpuhw;
> -- 
> 2.7.4
> 
>