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From: Conor Dooley <>
To: Andrew Bresticker <>
Cc: Palmer Dabbelt <>,
	Paul Walmsley <>,
	Celeste Liu <>,
	dram <>, Ruizhe Pan <>,,,
Subject: Re: [PATCH v4 0/2] Make mmap() with PROT_WRITE imply PROT_READ
Date: Tue, 11 Oct 2022 18:04:02 +0100	[thread overview]
Message-ID: <Y0WiAgnN5IcQDrez@spud> (raw)
In-Reply-To: <>

Hey Palmer,

On Thu, Sep 15, 2022 at 03:37:00PM -0400, Andrew Bresticker wrote:
> Commit 2139619bcad7 ("riscv: mmap with PROT_WRITE but no PROT_READ is
> invalid") made mmap() reject mappings with only PROT_WRITE set in an
> attempt to fix an observed inconsistency in behavior when attempting
> to read from a PROT_WRITE-only mapping. The root cause of this behavior
> was actually that while RISC-V's protection_map maps VM_WRITE to
> readable PTE permissions (since write-only PTEs are considered reserved
> by the privileged spec), the page fault handler considered loads from
> VM_WRITE-only VMAs illegal accesses. Fix the underlying cause by
> handling faults in VM_WRITE-only VMAs (patch 1) and then re-enable
> use of mmap(PROT_WRITE) (patch 2), making RISC-V's behavior consistent
> with all other architectures that don't support write-only PTEs.
> Both patches are tagged as fixes for the aforementioned commit since that
> commit made a userspace visible change that will break any software relying
> on mmap(PROT_WRITE). (Also cc: stable since the offending commit was
> itself backported to stable).

The patch that these commits fix has hit the distros & manifests as a
userspace breakage for openJDK:

Eva tested these patches and reported that their problem was fixed:

I asked them for a T-b but I don't see one on lore etc, but it would be
from Eva Kotova <> if you consider their
comments their sufficient for a T-B


> v1 -> v2: Allow handling of load faults in VM_WRITE VMAs
> v2 -> v3: Split into two pathces
> v3 -> v4: Fixes tags (+ this cover letter)
> Andrew Bresticker (2):
>   riscv: Make VM_WRITE imply VM_READ
>   riscv: Allow PROT_WRITE-only mmap()
>  arch/riscv/kernel/sys_riscv.c | 3 ---
>  arch/riscv/mm/fault.c         | 3 ++-
>  2 files changed, 2 insertions(+), 4 deletions(-)
> -- 
> 2.25.1
> _______________________________________________
> linux-riscv mailing list

linux-riscv mailing list

  parent reply	other threads:[~2022-10-11 17:04 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-09-15 19:37 [PATCH v4 0/2] Make mmap() with PROT_WRITE imply PROT_READ Andrew Bresticker
2022-09-15 19:37 ` [PATCH v4 1/2] riscv: Make VM_WRITE imply VM_READ Andrew Bresticker
2022-09-15 19:37 ` [PATCH v4 2/2] riscv: Allow PROT_WRITE-only mmap() Andrew Bresticker
2022-10-11 17:04 ` Conor Dooley [this message]
2022-10-13 21:01 ` [PATCH v4 0/2] Make mmap() with PROT_WRITE imply PROT_READ Palmer Dabbelt

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