On Mon, Feb 15, 2021 at 01:13:03PM +0000, Catalin Marinas wrote:
commit 68d54ceeec0e5fee4fb8048e6a04c193f32525ca upstream.
The ptrace(PTRACE_PEEKMTETAGS) implementation checks whether the user page has valid tags (mapped with PROT_MTE) by testing the PG_mte_tagged page flag. If this bit is cleared, ptrace(PTRACE_PEEKMTETAGS) returns -EIO.
A newly created (PROT_MTE) mapping points to the zero page which had its tags zeroed during cpu_enable_mte(). If there were no prior writes to this mapping, ptrace(PTRACE_PEEKMTETAGS) fails with -EIO since the zero page does not have the PG_mte_tagged flag set.
Set PG_mte_tagged on the zero page when its tags are cleared during boot. In addition, to avoid ptrace(PTRACE_PEEKMTETAGS) succeeding on !PROT_MTE mappings pointing to the zero page, change the __access_remote_tags() check to (vm_flags & VM_MTE) instead of PG_mte_tagged.
Signed-off-by: Catalin Marinas catalin.marinas@arm.com Fixes: 34bfeea4a9e9 ("arm64: mte: Clear the tags when a page is mapped in user-space with PROT_MTE") Cc: stable@vger.kernel.org # 5.10.x Cc: Will Deacon will@kernel.org Reported-by: Luis Machado luis.machado@linaro.org Tested-by: Luis Machado luis.machado@linaro.org Reviewed-by: Vincenzo Frascino vincenzo.frascino@arm.com Link: https://lore.kernel.org/r/20210210180316.23654-1-catalin.marinas@arm.com
arch/arm64/kernel/cpufeature.c | 6 +----- arch/arm64/kernel/mte.c | 3 ++- 2 files changed, 3 insertions(+), 6 deletions(-)
Thanks, now queued up.
greg k-h