linux-kernel - [PATCH 1/5] perf/x86/intel/pt: Relax address filter validation

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Date:   Mon, 31 Jan 2022 09:24:49 +0200
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...hat.com>, linux-kernel@...r.kernel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        kvm@...r.kernel.org, H Peter Anvin <hpa@...or.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Leo Yan <leo.yan@...aro.org>
Subject: [PATCH 1/5] perf/x86/intel/pt: Relax address filter validation

The requirement for 64-bit address filters is that they are canonical
addresses. In other respects any address range is allowed which would
include user space addresses.

That can be useful for tracing virtual machine guests because address
filtering can be used to advantage in place of current privilege level
(CPL) filtering.

Signed-off-by: Adrian Hunter <adrian.hunter@...el.com>
---
 arch/x86/events/intel/pt.c | 63 ++++++++++++++++++++++++++++++--------
 1 file changed, 50 insertions(+), 13 deletions(-)

diff --git a/arch/x86/events/intel/pt.c b/arch/x86/events/intel/pt.c
index ae396fdfabab..4443de56a2d5 100644
--- a/arch/x86/events/intel/pt.c
+++ b/arch/x86/events/intel/pt.c
@@ -13,6 +13,8 @@
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
 #include <linux/types.h>
+#include <linux/bits.h>
+#include <linux/limits.h>
 #include <linux/slab.h>
 #include <linux/device.h>
 
@@ -1363,11 +1365,37 @@ static void pt_addr_filters_fini(struct perf_event *event)
 	event->hw.addr_filters = NULL;
 }
 
-static inline bool valid_kernel_ip(unsigned long ip)
+#ifdef CONFIG_X86_64
+static u64 canonical_address(u64 vaddr, u8 vaddr_bits)
 {
-	return virt_addr_valid(ip) && kernel_ip(ip);
+	return ((s64)vaddr << (64 - vaddr_bits)) >> (64 - vaddr_bits);
 }
 
+static u64 is_canonical_address(u64 vaddr, u8 vaddr_bits)
+{
+	return canonical_address(vaddr, vaddr_bits) == vaddr;
+}
+
+/* Clamp to a canonical address greater-than-or-equal-to the address given */
+static u64 clamp_to_ge_canonical_addr(u64 vaddr, u8 vaddr_bits)
+{
+	return is_canonical_address(vaddr, vaddr_bits) ?
+	       vaddr :
+	       -BIT_ULL(vaddr_bits - 1);
+}
+
+/* Clamp to a canonical address less-than-or-equal-to the address given */
+static u64 clamp_to_le_canonical_addr(u64 vaddr, u8 vaddr_bits)
+{
+	return is_canonical_address(vaddr, vaddr_bits) ?
+	       vaddr :
+	       BIT_ULL(vaddr_bits - 1) - 1;
+}
+#else
+#define clamp_to_ge_canonical_addr(x, y) (x)
+#define clamp_to_le_canonical_addr(x, y) (x)
+#endif
+
 static int pt_event_addr_filters_validate(struct list_head *filters)
 {
 	struct perf_addr_filter *filter;
@@ -1382,14 +1410,6 @@ static int pt_event_addr_filters_validate(struct list_head *filters)
 		    filter->action == PERF_ADDR_FILTER_ACTION_START)
 			return -EOPNOTSUPP;
 
-		if (!filter->path.dentry) {
-			if (!valid_kernel_ip(filter->offset))
-				return -EINVAL;
-
-			if (!valid_kernel_ip(filter->offset + filter->size))
-				return -EINVAL;
-		}
-
 		if (++range > intel_pt_validate_hw_cap(PT_CAP_num_address_ranges))
 			return -EOPNOTSUPP;
 	}
@@ -1413,9 +1433,26 @@ static void pt_event_addr_filters_sync(struct perf_event *event)
 		if (filter->path.dentry && !fr[range].start) {
 			msr_a = msr_b = 0;
 		} else {
-			/* apply the offset */
-			msr_a = fr[range].start;
-			msr_b = msr_a + fr[range].size - 1;
+			unsigned long n = fr[range].size - 1;
+			unsigned long a = fr[range].start;
+			unsigned long b;
+
+			if (a > ULONG_MAX - n)
+				b = ULONG_MAX;
+			else
+				b = a + n;
+			/*
+			 * Apply the offset. 64-bit addresses written to the
+			 * MSRs must be canonical, but the range can encompass
+			 * non-canonical addresses. Since software cannot
+			 * execute at non-canonical addresses, adjusting to
+			 * canonical addresses does not affect the result of the
+			 * address filter.
+			 */
+			msr_a = clamp_to_ge_canonical_addr(a, boot_cpu_data.x86_virt_bits);
+			msr_b = clamp_to_le_canonical_addr(b, boot_cpu_data.x86_virt_bits);
+			if (msr_b < msr_a)
+				msr_a = msr_b = 0;
 		}
 
 		filters->filter[range].msr_a  = msr_a;
-- 
2.25.1