From: Charlie Jenkins <charlie@rivosinc.com>
To: Andreas Schwab <schwab@linux-m68k.org>
Cc: Emil Renner Berthing <emil.renner.berthing@canonical.com>,
linux-riscv@lists.infradead.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org,
Eric Biederman <ebiederm@xmission.com>,
Kees Cook <keescook@chromium.org>,
Paul Walmsley <paul.walmsley@sifive.com>,
Palmer Dabbelt <palmer@dabbelt.com>,
Albert Ou <aou@eecs.berkeley.edu>,
Samuel Holland <samuel.holland@sifive.com>,
Nelson Chu <nelson@rivosinc.com>,
Emil Renner Berthing <kernel@esmil.dk>
Subject: Re: [PATCH v7 1/3] riscv: Avoid unaligned access when relocating modules
Date: Tue, 31 Oct 2023 13:06:39 -0700 [thread overview]
Message-ID: <ZUFeTzStw1qaM0m+@ghost> (raw)
In-Reply-To: <878r7iiwb6.fsf@igel.home>
On Tue, Oct 31, 2023 at 05:35:57PM +0100, Andreas Schwab wrote:
> On Okt 31 2023, Emil Renner Berthing wrote:
>
> >> +static int riscv_insn_rmw(void *location, u32 keep, u32 set)
> >> +{
> >> + u16 *parcel = location;
> >> + u32 insn = (u32)le16_to_cpu(parcel[0]) | (u32)le16_to_cpu(parcel[1]) << 16;
> >> +
> >> + insn &= keep;
> >> + insn |= set;
> >> +
> >> + parcel[0] = cpu_to_le32(insn);
> >
> > Why cpu_to_le32(insn)? Unless I've misunderstood something downcasting unsigned
> > to unsigned values in C (eg. from u32 to u16) is defined to always discard the
> > most signifcant bits, so cpu_to_le16(insn) should be fine.
>
> cpu_to_le32(insn) can't be right here anyway, since it also swaps the
> two u16 halves and would be the same as cpu_to_le16(insn >> 16) on big
> endian.
Yes, not sure why I did that... I will fix that up.
- Charlie
>
> --
> Andreas Schwab, schwab@linux-m68k.org
> GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510 2552 DF73 E780 A9DA AEC1
> "And now for something completely different."
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WARNING: multiple messages have this Message-ID (diff)
From: Charlie Jenkins <charlie@rivosinc.com>
To: Andreas Schwab <schwab@linux-m68k.org>
Cc: Emil Renner Berthing <emil.renner.berthing@canonical.com>,
linux-riscv@lists.infradead.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org,
Eric Biederman <ebiederm@xmission.com>,
Kees Cook <keescook@chromium.org>,
Paul Walmsley <paul.walmsley@sifive.com>,
Palmer Dabbelt <palmer@dabbelt.com>,
Albert Ou <aou@eecs.berkeley.edu>,
Samuel Holland <samuel.holland@sifive.com>,
Nelson Chu <nelson@rivosinc.com>,
Emil Renner Berthing <kernel@esmil.dk>
Subject: Re: [PATCH v7 1/3] riscv: Avoid unaligned access when relocating modules
Date: Tue, 31 Oct 2023 13:06:39 -0700 [thread overview]
Message-ID: <ZUFeTzStw1qaM0m+@ghost> (raw)
In-Reply-To: <878r7iiwb6.fsf@igel.home>
On Tue, Oct 31, 2023 at 05:35:57PM +0100, Andreas Schwab wrote:
> On Okt 31 2023, Emil Renner Berthing wrote:
>
> >> +static int riscv_insn_rmw(void *location, u32 keep, u32 set)
> >> +{
> >> + u16 *parcel = location;
> >> + u32 insn = (u32)le16_to_cpu(parcel[0]) | (u32)le16_to_cpu(parcel[1]) << 16;
> >> +
> >> + insn &= keep;
> >> + insn |= set;
> >> +
> >> + parcel[0] = cpu_to_le32(insn);
> >
> > Why cpu_to_le32(insn)? Unless I've misunderstood something downcasting unsigned
> > to unsigned values in C (eg. from u32 to u16) is defined to always discard the
> > most signifcant bits, so cpu_to_le16(insn) should be fine.
>
> cpu_to_le32(insn) can't be right here anyway, since it also swaps the
> two u16 halves and would be the same as cpu_to_le16(insn >> 16) on big
> endian.
Yes, not sure why I did that... I will fix that up.
- Charlie
>
> --
> Andreas Schwab, schwab@linux-m68k.org
> GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510 2552 DF73 E780 A9DA AEC1
> "And now for something completely different."
next prev parent reply other threads:[~2023-10-31 20:07 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-10-31 7:24 [PATCH v7 0/3] riscv: Add remaining module relocations and tests Charlie Jenkins
2023-10-31 7:24 ` Charlie Jenkins
2023-10-31 7:24 ` [PATCH v7 1/3] riscv: Avoid unaligned access when relocating modules Charlie Jenkins
2023-10-31 7:24 ` Charlie Jenkins
2023-10-31 13:11 ` Emil Renner Berthing
2023-10-31 13:11 ` Emil Renner Berthing
2023-10-31 16:35 ` Andreas Schwab
2023-10-31 16:35 ` Andreas Schwab
2023-10-31 20:06 ` Charlie Jenkins [this message]
2023-10-31 20:06 ` Charlie Jenkins
2023-10-31 7:24 ` [PATCH v7 2/3] riscv: Add remaining module relocations Charlie Jenkins
2023-10-31 7:24 ` Charlie Jenkins
2023-10-31 13:43 ` Emil Renner Berthing
2023-10-31 13:43 ` Emil Renner Berthing
2023-10-31 18:18 ` Charlie Jenkins
2023-10-31 18:18 ` Charlie Jenkins
2023-10-31 7:24 ` [PATCH v7 3/3] riscv: Add tests for riscv module loading Charlie Jenkins
2023-10-31 7:24 ` Charlie Jenkins
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