linux-kernel - [PATCH v2] tpm: use GFP kernel for tpm

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Message-ID: <1570809779.24157.1.camel@HansenPartnership.com>
Date:   Fri, 11 Oct 2019 09:02:59 -0700
From:   James Bottomley <James.Bottomley@...senPartnership.com>
To:     linux-integrity@...r.kernel.org
Cc:     open list <linux-kernel@...r.kernel.org>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        Jerry Snitselaar <jsnitsel@...hat.com>
Subject: [PATCH v2] tpm: use GFP kernel for tpm_buf allocations

The current code uses GFP_HIGHMEM, which is wrong because GFP_HIGHMEM
(on 32 bit systems) is memory ordinarily inaccessible to the kernel
and should only be used for allocations affecting userspace.  In order
to make highmem visible to the kernel on 32 bit it has to be kmapped,
which consumes valuable entries in the kmap region.  Since the tpm_buf
is only ever used in the kernel, switch to using a GFP_KERNEL
allocation so as not to waste kmap space on 32 bits.

Fixes: a74f8b36352e (tpm: introduce tpm_buf)
Reviewed-by: Jerry Snitselaar <jsnitsel@...hat.com>
Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Signed-off-by: James Bottomley <James.Bottomley@...senPartnership.com>

---

v2: fix 0day spotted problem with free_page taking an unsigned long
    not a void *
---
 drivers/char/tpm/tpm.h | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/drivers/char/tpm/tpm.h b/drivers/char/tpm/tpm.h
index a7fea3e0ca86..3a7998d7309a 100644
--- a/drivers/char/tpm/tpm.h
+++ b/drivers/char/tpm/tpm.h
@@ -284,7 +284,6 @@ enum tpm_buf_flags {
 };
 
 struct tpm_buf {
-	struct page *data_page;
 	unsigned int flags;
 	u8 *data;
 };
@@ -300,20 +299,18 @@ static inline void tpm_buf_reset(struct tpm_buf *buf, u16 tag, u32 ordinal)
 
 static inline int tpm_buf_init(struct tpm_buf *buf, u16 tag, u32 ordinal)
 {
-	buf->data_page = alloc_page(GFP_HIGHUSER);
-	if (!buf->data_page)
+	buf->data = (u8 *)__get_free_page(GFP_KERNEL);
+	if (!buf->data)
 		return -ENOMEM;
 
 	buf->flags = 0;
-	buf->data = kmap(buf->data_page);
 	tpm_buf_reset(buf, tag, ordinal);
 	return 0;
 }
 
 static inline void tpm_buf_destroy(struct tpm_buf *buf)
 {
-	kunmap(buf->data_page);
-	__free_page(buf->data_page);
+	free_page((unsigned long)buf->data);
 }
 
 static inline u32 tpm_buf_length(struct tpm_buf *buf)
-- 
2.16.4