linux-kernel - Re: [PATCH] firmware: qcom: scm: Fix crash in qcom_scm_call

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Date:   Tue, 10 Apr 2018 18:55:04 -0700
From:   Stephen Boyd <sboyd@...nel.org>
To:     Andy Gross <andy.gross@...aro.org>,
        Avaneesh Kumar Dwivedi <akdwived@...eaurora.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Niklas Cassel <niklas.cassel@...aro.org>,
        Stephen Boyd <sboyd@...eaurora.org>
Cc:     linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] firmware: qcom: scm: Fix crash in qcom_scm_call_atomic1()

Quoting Niklas Cassel (2018-04-09 14:40:15)
> qcom_scm_call_atomic1() can crash with a NULL pointer dereference at
> qcom_scm_call_atomic1+0x30/0x48.
> 
> disassembly of qcom_scm_call_atomic1():
> ...
> <0xc08d73b0 <+12>: ldr r3, [r12]
> ... (no instruction explicitly modifies r12)
> 0xc08d73cc <+40>: smc 0
> ... (no instruction explicitly modifies r12)
> 0xc08d73d4 <+48>: ldr r3, [r12] <- crashing instruction
> ...
> 
> Since the first ldr is successful, and since r12 isn't explicitly
> modified by any instruction between the first and the second ldr,
> it must have been modified by the smc call, which is ok,
> since r12 is caller save according to the AAPCS.
> 
> Add r12 to the clobber list so that the compiler knows that the
> callee potentially overwrites the value in r12.
> Clobber descriptions may not in any way overlap with an input or
> output operand.
> 
> Signed-off-by: Niklas Cassel <niklas.cassel@...aro.org>
> ---

Reviewed-by: Stephen Boyd <sboyd@...nel.org>