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c=relaxed/simple; d=kernel.org; s=k20201202; t=1686760240; bh=BTRpdtoeEYlLDtLE5Hz7bt0AbC5snDe5AP82plYvJB4=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=MhOQgO8G7rjuCicC7gc96DgmWWy5WmsW0DPUJAHvRFytzAflm2xm/wTrFaJiKc5QR /ucL6nOYDR+QO7DpHsmcygaAaASqwz4lC+0uQAU9ylqrB88mAOD5mU4HW6+5RR3/Sq BuevYHU8Rhd44fxypacea7cRdKgB0oXwbZj4qRbBBSX4+jR98pCfiebWP5P6RRR3ui 7woSZEChE9xIRJI8rJnXknXln3W0PtKEfujbIholja0O0vCXlrQ/P+P+8mDcpkxFwv 8+DnTNZ9DkBBzZh3WDvIA3fJusUpTF9on5k+Lk2ZZIRyZzq8xkxfXood8rIvnNFhfp Rb0bOAtfaV5gQ== Date: Wed, 14 Jun 2023 17:30:34 +0100 From: Lee Jones To: dave.hansen@linux.intel.com, luto@kernel.org, peterz@infradead.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, x86@kernel.org, hpa@zytor.com, linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/1] x86/mm/KASLR: Store pud_page_tramp into entry rather than page Message-ID: <20230614163034.GB3635807@google.com> References: <20230614155223.905222-1-lee@kernel.org> <20230614155223.905222-2-lee@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20230614155223.905222-2-lee@kernel.org> X-Rspamd-Queue-Id: C2EAB180029 X-Rspam-User: X-Rspamd-Server: rspam04 X-Stat-Signature: q1y33hrutpwz8t6j4mfnrja8xax8s14s X-HE-Tag: 1686760241-819516 X-HE-Meta: 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 3G/uDSWo pKOhDGNYmUDps2yJOnj7YcH+Pud9AmetylBrjbd/hK3Ke3TkVwKzzSM6djIFdbB1Qoo8AIc/oUbSw+7dZAc5SULi3SpKJxq//DBQoK+m31Svo2vrCQB5bUNzXaHxPqfmIENweZPeuToZI2fKBmYMeRLB3H2ZbWzQ2TkDCZRiyEi6o7VlRx7RLMfe7p0HRgXcZ3+jzknPvRFRBjIwY/sYecnKoTJQJKxnQ125MbFV6/HdbM7AhBG9woBKF4ISb4YLjM5JSEowQ1dLEjmq+Nm7DmfqO9A7nmx/lCps45yX/vozXX7KIkD8AMwMAyVNy9vU94AqsQ0XA6zX0H+fWPO67LoJOkrz5AcZ6rDHjXuvH3Wzz1LDYxwS7n1/ssw== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, 14 Jun 2023, Lee Jones wrote: > set_pgd() expects to be passed whole pages to operate on, whereas > trampoline_pgd_entry is, as the name suggests, an entry. The > ramifications for using set_pgd() here are that the following thread of > execution will not only place the suggested value into the > trampoline_pgd_entry (8-Byte globally stored [.bss]) variable, PTI will > also attempt to replicate that value into the non-existent neighboring > user page (located +4k away), leading to the corruption of other global > [.bss] stored variables. > > Suggested-by: Dave Hansen > Signed-off-by: Lee Jones > --- > arch/x86/mm/kaslr.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/mm/kaslr.c b/arch/x86/mm/kaslr.c > index 557f0fe25dff4..ee6f22f3385b6 100644 > --- a/arch/x86/mm/kaslr.c > +++ b/arch/x86/mm/kaslr.c > @@ -175,7 +175,7 @@ void __meminit init_trampoline_kaslr(void) > set_pgd(&trampoline_pgd_entry, > __pgd(_KERNPG_TABLE | __pa(p4d_page_tramp))); This needs converting too. v2 in test. > } else { > - set_pgd(&trampoline_pgd_entry, > - __pgd(_KERNPG_TABLE | __pa(pud_page_tramp))); > + trampoline_pgd_entry = > + __pgd(_KERNPG_TABLE | __pa(pud_page_tramp)); > } > } -- Lee Jones [李琼斯]