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authorNicholas Piggin <npiggin@gmail.com>2020-11-17 16:59:13 +1100
committerMichael Ellerman <mpe@ellerman.id.au>2020-11-19 23:47:18 +1100
commit9a32a7e78bd0cd9a9b6332cbdc345ee5ffd0c5de (patch)
treee9f7d6a2b72ddc59cb30cc87a36e635c2e0ab243 /arch/powerpc/lib/feature-fixups.c
parentf79643787e0a0762d2409b7b8334e83f22d85695 (diff)
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powerpc/64s: flush L1D after user accesses
IBM Power9 processors can speculatively operate on data in the L1 cache before it has been completely validated, via a way-prediction mechanism. It is not possible for an attacker to determine the contents of impermissible memory using this method, since these systems implement a combination of hardware and software security measures to prevent scenarios where protected data could be leaked. However these measures don't address the scenario where an attacker induces the operating system to speculatively execute instructions using data that the attacker controls. This can be used for example to speculatively bypass "kernel user access prevention" techniques, as discovered by Anthony Steinhauser of Google's Safeside Project. This is not an attack by itself, but there is a possibility it could be used in conjunction with side-channels or other weaknesses in the privileged code to construct an attack. This issue can be mitigated by flushing the L1 cache between privilege boundaries of concern. This patch flushes the L1 cache after user accesses. This is part of the fix for CVE-2020-4788. Signed-off-by: Nicholas Piggin <npiggin@gmail.com> Signed-off-by: Daniel Axtens <dja@axtens.net> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Diffstat (limited to 'arch/powerpc/lib/feature-fixups.c')
-rw-r--r--arch/powerpc/lib/feature-fixups.c50
1 files changed, 50 insertions, 0 deletions
diff --git a/arch/powerpc/lib/feature-fixups.c b/arch/powerpc/lib/feature-fixups.c
index 70e83cfd74aa..321c12a9ef6b 100644
--- a/arch/powerpc/lib/feature-fixups.c
+++ b/arch/powerpc/lib/feature-fixups.c
@@ -234,6 +234,56 @@ void do_stf_barrier_fixups(enum stf_barrier_type types)
do_stf_exit_barrier_fixups(types);
}
+void do_uaccess_flush_fixups(enum l1d_flush_type types)
+{
+ unsigned int instrs[4], *dest;
+ long *start, *end;
+ int i;
+
+ start = PTRRELOC(&__start___uaccess_flush_fixup);
+ end = PTRRELOC(&__stop___uaccess_flush_fixup);
+
+ instrs[0] = 0x60000000; /* nop */
+ instrs[1] = 0x60000000; /* nop */
+ instrs[2] = 0x60000000; /* nop */
+ instrs[3] = 0x4e800020; /* blr */
+
+ i = 0;
+ if (types == L1D_FLUSH_FALLBACK) {
+ instrs[3] = 0x60000000; /* nop */
+ /* fallthrough to fallback flush */
+ }
+
+ if (types & L1D_FLUSH_ORI) {
+ instrs[i++] = 0x63ff0000; /* ori 31,31,0 speculation barrier */
+ instrs[i++] = 0x63de0000; /* ori 30,30,0 L1d flush*/
+ }
+
+ if (types & L1D_FLUSH_MTTRIG)
+ instrs[i++] = 0x7c12dba6; /* mtspr TRIG2,r0 (SPR #882) */
+
+ for (i = 0; start < end; start++, i++) {
+ dest = (void *)start + *start;
+
+ pr_devel("patching dest %lx\n", (unsigned long)dest);
+
+ patch_instruction((struct ppc_inst *)dest, ppc_inst(instrs[0]));
+
+ patch_instruction((struct ppc_inst *)(dest + 1), ppc_inst(instrs[1]));
+ patch_instruction((struct ppc_inst *)(dest + 2), ppc_inst(instrs[2]));
+ patch_instruction((struct ppc_inst *)(dest + 3), ppc_inst(instrs[3]));
+ }
+
+ printk(KERN_DEBUG "uaccess-flush: patched %d locations (%s flush)\n", i,
+ (types == L1D_FLUSH_NONE) ? "no" :
+ (types == L1D_FLUSH_FALLBACK) ? "fallback displacement" :
+ (types & L1D_FLUSH_ORI) ? (types & L1D_FLUSH_MTTRIG)
+ ? "ori+mttrig type"
+ : "ori type" :
+ (types & L1D_FLUSH_MTTRIG) ? "mttrig type"
+ : "unknown");
+}
+
void do_entry_flush_fixups(enum l1d_flush_type types)
{
unsigned int instrs[3], *dest;