Re: [PATCH] powerpc: Add build-time check of ptrace PT_xx defines

[Christophe Leroy <christophe.leroy@c-s.fr>]

Le 30/10/2019 à 12:12, Michael Ellerman a écrit :
> As part of the uapi we export a lot of PT_xx defines for each register
> in struct pt_regs. These are expressed as an index from gpr[0], in
> units of unsigned long.
> 
> Currently there's nothing tying the values of those defines to the
> actual layout of the struct.
> 
> But we *don't* want to change the uapi defines to derive the PT_xx
> values based on the layout of the struct, those values are ABI and
> must never change.
> 
> Instead we want to do the reverse, make sure that the layout of the
> struct never changes vs the PT_xx defines. So add build time checks of
> that.
> 
> This probably seems paranoid, but at least once in the past someone
> has sent a patch that would have broken the ABI if it hadn't been
> spotted. Although it probably would have been detected via testing,
> it's preferable to just quash any issues at the source.

While you are playing with pt_regs_check(), could you also take the 
patch from Mathieu https://patchwork.ozlabs.org/patch/1009816/ ?

Christophe

> 
> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
> ---
>   arch/powerpc/kernel/ptrace.c | 63 ++++++++++++++++++++++++++++++++++++
>   1 file changed, 63 insertions(+)
> 
> diff --git a/arch/powerpc/kernel/ptrace.c b/arch/powerpc/kernel/ptrace.c
> index 8c92febf5f44..abd888bada03 100644
> --- a/arch/powerpc/kernel/ptrace.c
> +++ b/arch/powerpc/kernel/ptrace.c
> @@ -3398,4 +3398,67 @@ void __init pt_regs_check(void)
>   		     offsetof(struct user_pt_regs, result));
>   
>   	BUILD_BUG_ON(sizeof(struct user_pt_regs) > sizeof(struct pt_regs));
> +
> +	// Now check that the pt_regs offsets match the uapi #defines
> +	#define CHECK_REG(_pt, _reg) \
> +		BUILD_BUG_ON(_pt != (offsetof(struct user_pt_regs, _reg) / \
> +				     sizeof(unsigned long)));
> +
> +	CHECK_REG(PT_R0,  gpr[0]);
> +	CHECK_REG(PT_R1,  gpr[1]);
> +	CHECK_REG(PT_R2,  gpr[2]);
> +	CHECK_REG(PT_R3,  gpr[3]);
> +	CHECK_REG(PT_R4,  gpr[4]);
> +	CHECK_REG(PT_R5,  gpr[5]);
> +	CHECK_REG(PT_R6,  gpr[6]);
> +	CHECK_REG(PT_R7,  gpr[7]);
> +	CHECK_REG(PT_R8,  gpr[8]);
> +	CHECK_REG(PT_R9,  gpr[9]);
> +	CHECK_REG(PT_R10, gpr[10]);
> +	CHECK_REG(PT_R11, gpr[11]);
> +	CHECK_REG(PT_R12, gpr[12]);
> +	CHECK_REG(PT_R13, gpr[13]);
> +	CHECK_REG(PT_R14, gpr[14]);
> +	CHECK_REG(PT_R15, gpr[15]);
> +	CHECK_REG(PT_R16, gpr[16]);
> +	CHECK_REG(PT_R17, gpr[17]);
> +	CHECK_REG(PT_R18, gpr[18]);
> +	CHECK_REG(PT_R19, gpr[19]);
> +	CHECK_REG(PT_R20, gpr[20]);
> +	CHECK_REG(PT_R21, gpr[21]);
> +	CHECK_REG(PT_R22, gpr[22]);
> +	CHECK_REG(PT_R23, gpr[23]);
> +	CHECK_REG(PT_R24, gpr[24]);
> +	CHECK_REG(PT_R25, gpr[25]);
> +	CHECK_REG(PT_R26, gpr[26]);
> +	CHECK_REG(PT_R27, gpr[27]);
> +	CHECK_REG(PT_R28, gpr[28]);
> +	CHECK_REG(PT_R29, gpr[29]);
> +	CHECK_REG(PT_R30, gpr[30]);
> +	CHECK_REG(PT_R31, gpr[31]);
> +	CHECK_REG(PT_NIP, nip);
> +	CHECK_REG(PT_MSR, msr);
> +	CHECK_REG(PT_ORIG_R3, orig_gpr3);
> +	CHECK_REG(PT_CTR, ctr);
> +	CHECK_REG(PT_LNK, link);
> +	CHECK_REG(PT_XER, xer);
> +	CHECK_REG(PT_CCR, ccr);
> +#ifdef CONFIG_PPC64
> +	CHECK_REG(PT_SOFTE, softe);
> +#else
> +	CHECK_REG(PT_MQ, mq);
> +#endif
> +	CHECK_REG(PT_TRAP, trap);
> +	CHECK_REG(PT_DAR, dar);
> +	CHECK_REG(PT_DSISR, dsisr);
> +	CHECK_REG(PT_RESULT, result);
> +	#undef CHECK_REG
> +
> +	BUILD_BUG_ON(PT_REGS_COUNT != sizeof(struct user_pt_regs) / sizeof(unsigned long));
> +
> +	/*
> +	 * PT_DSCR isn't a real reg, but it's important that it doesn't overlap the
> +	 * real registers.
> +	 */
> +	BUILD_BUG_ON(PT_DSCR < sizeof(struct user_pt_regs) / sizeof(unsigned long));
>   }
>