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| author | Russell King <rmk+kernel@armlinux.org.uk> | 2018-05-14 10:40:24 +0200 |
|---|---|---|
| committer | Russell King <rmk+kernel@armlinux.org.uk> | 2018-08-02 18:41:38 +0200 |
| commit | a3c0f84765bb429ba0fd23de1c57b5e1591c9389 (patch) | |
| tree | 993cc81b042f839d871122c5ed4bf3b1c5770d2f /arch/arm | |
| parent | ARM: spectre-v1: use get_user() for __get_user() (diff) | |
| download | linux-a3c0f84765bb429ba0fd23de1c57b5e1591c9389.tar.xz linux-a3c0f84765bb429ba0fd23de1c57b5e1591c9389.zip | |
ARM: spectre-v1: mitigate user accesses
Spectre variant 1 attacks are about this sequence of pseudo-code:
index = load(user-manipulated pointer);
access(base + index * stride);
In order for the cache side-channel to work, the access() must me made
to memory which userspace can detect whether cache lines have been
loaded. On 32-bit ARM, this must be either user accessible memory, or
a kernel mapping of that same user accessible memory.
The problem occurs when the load() speculatively loads privileged data,
and the subsequent access() is made to user accessible memory.
Any load() which makes use of a user-maniplated pointer is a potential
problem if the data it has loaded is used in a subsequent access. This
also applies for the access() if the data loaded by that access is used
by a subsequent access.
Harden the get_user() accessors against Spectre attacks by forcing out
of bounds addresses to a NULL pointer. This prevents get_user() being
used as the load() step above. As a side effect, put_user() will also
be affected even though it isn't implicated.
Also harden copy_from_user() by redoing the bounds check within the
arm_copy_from_user() code, and NULLing the pointer if out of bounds.
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Diffstat (limited to 'arch/arm')
| -rw-r--r-- | arch/arm/include/asm/assembler.h | 4 | ||||
| -rw-r--r-- | arch/arm/lib/copy_from_user.S | 9 |
2 files changed, 13 insertions, 0 deletions
diff --git a/arch/arm/include/asm/assembler.h b/arch/arm/include/asm/assembler.h index ef1386b1af9b..f0515f60cff5 100644 --- a/arch/arm/include/asm/assembler.h +++ b/arch/arm/include/asm/assembler.h @@ -460,6 +460,10 @@ THUMB( orr \reg , \reg , #PSR_T_BIT ) adds \tmp, \addr, #\size - 1 sbcccs \tmp, \tmp, \limit bcs \bad +#ifdef CONFIG_CPU_SPECTRE + movcs \addr, #0 + csdb +#endif #endif .endm diff --git a/arch/arm/lib/copy_from_user.S b/arch/arm/lib/copy_from_user.S index 7a4b06049001..a826df3d3814 100644 --- a/arch/arm/lib/copy_from_user.S +++ b/arch/arm/lib/copy_from_user.S @@ -90,6 +90,15 @@ .text ENTRY(arm_copy_from_user) +#ifdef CONFIG_CPU_SPECTRE + get_thread_info r3 + ldr r3, [r3, #TI_ADDR_LIMIT] + adds ip, r1, r2 @ ip=addr+size + sub r3, r3, #1 @ addr_limit - 1 + cmpcc ip, r3 @ if (addr+size > addr_limit - 1) + movcs r1, #0 @ addr = NULL + csdb +#endif #include "copy_template.S" |