linux-kernel - Re: [PATCH v4 0/9] powerpc: Switch to CONFIG_THREAD_INFO_IN

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Date:   Sat, 06 Oct 2018 22:21:30 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Christophe Leroy <christophe.leroy@....fr>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v4 0/9] powerpc: Switch to CONFIG_THREAD_INFO_IN_TASK

Christophe Leroy <christophe.leroy@....fr> writes:

> The purpose of this serie is to activate CONFIG_THREAD_INFO_IN_TASK which
> moves the thread_info into task_struct.
>
> Moving thread_info into task_struct has the following advantages:
> - It protects thread_info from corruption in the case of stack
> overflows.
> - Its address is harder to determine if stack addresses are
> leaked, making a number of attacks more difficult.

We need to fixup bpf_jit32.h:

#ifdef CONFIG_SMP
#ifdef CONFIG_PPC64
#define PPC_BPF_LOAD_CPU(r)		\
	do { BUILD_BUG_ON(FIELD_SIZEOF(struct paca_struct, paca_index) != 2);	\
		PPC_LHZ_OFFS(r, 13, offsetof(struct paca_struct, paca_index));	\
	} while (0)
#else
#define PPC_BPF_LOAD_CPU(r)     \
	do { BUILD_BUG_ON(FIELD_SIZEOF(struct thread_info, cpu) != 4);		\
		PPC_LHZ_OFFS(r, (1 & ~(THREAD_SIZE - 1)),			\
				offsetof(struct thread_info, cpu));		\
	} while(0)
#endif
#else
#define PPC_BPF_LOAD_CPU(r) do { PPC_LI(r, 0); } while(0)
#endif


cheers