Re: [PATCH v23 06/28] riscv/mm : ensure PROT_WRITE leads to VM_READ | VM_WRITE

From: Andreas Schwab <schwab@linux-m68k.org>
To: Deepak Gupta via B4 Relay <devnull+debug.rivosinc.com@kernel.org>
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Subject: Re: [PATCH v23 06/28] riscv/mm : ensure PROT_WRITE leads to VM_READ | VM_WRITE
Date: Sat, 30 May 2026 17:02:35 +0200	[thread overview]
Message-ID: <87jyslndo4.fsf@igel.home> (raw)
In-Reply-To: <20251112-v5_user_cfi_series-v23-6-b55691eacf4f@rivosinc.com> (Deepak Gupta via's message of "Wed, 12 Nov 2025 16:43:04 -0800")

On Nov 12 2025, Deepak Gupta via B4 Relay wrote:

> From: Deepak Gupta <debug@rivosinc.com>
>
> `arch_calc_vm_prot_bits` is implemented on risc-v to return VM_READ |
> VM_WRITE if PROT_WRITE is specified. Similarly `riscv_sys_mmap` is
> updated to convert all incoming PROT_WRITE to (PROT_WRITE | PROT_READ).
> This is to make sure that any existing apps using PROT_WRITE still work.
>
> Earlier `protection_map[VM_WRITE]` used to pick read-write PTE encodings.
> Now `protection_map[VM_WRITE]` will always pick PAGE_SHADOWSTACK PTE
> encodings for shadow stack. Above changes ensure that existing apps
> continue to work because underneath kernel will be picking
> `protection_map[VM_WRITE|VM_READ]` PTE encodings.

This breaks LTP mmap04:

$ ./mmap04
tst_test.c:2042: TINFO: LTP version: 20260529.5ccf816f
tst_test.c:2045: TINFO: Tested kernel: 7.0.10-5-default #1 SMP PREEMPT_DYNAMIC Sat May 23 12:09:09 UTC 2026 (bb95589) riscv64
tst_kconfig.c:90: TINFO: Parsing kernel config '/proc/config.gz'
tst_kconfig.c:753: TINFO: CONFIG_FAULT_INJECTION kernel option detected which might slow the execution
tst_test.c:1870: TINFO: Overall timeout per run is 0h 04m 00s
mmap04.c:66: TPASS: mapping permissions in /proc matched: ---p
mmap04.c:66: TPASS: mapping permissions in /proc matched: ---s
mmap04.c:66: TPASS: mapping permissions in /proc matched: r--p
mmap04.c:66: TPASS: mapping permissions in /proc matched: r--s
mmap04.c:68: TFAIL: mapping permissions in /proc mismatched, expected: -w-p, found: rw-p
mmap04.c:68: TFAIL: mapping permissions in /proc mismatched, expected: -w-s, found: rw-s
mmap04.c:66: TPASS: mapping permissions in /proc matched: rw-p
mmap04.c:66: TPASS: mapping permissions in /proc matched: rw-s
mmap04.c:66: TPASS: mapping permissions in /proc matched: r-xp
mmap04.c:66: TPASS: mapping permissions in /proc matched: r-xs
mmap04.c:68: TFAIL: mapping permissions in /proc mismatched, expected: -wxp, found: rwxp
mmap04.c:68: TFAIL: mapping permissions in /proc mismatched, expected: -wxs, found: rwxs
mmap04.c:66: TPASS: mapping permissions in /proc matched: rwxp
mmap04.c:66: TPASS: mapping permissions in /proc matched: rwxs

Summary:
passed   10
failed   4
broken   0
skipped  0
warnings 0

-- 
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510  2552 DF73 E780 A9DA AEC1
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